diff --git a/Help/manual/cmake-variables.7.rst b/Help/manual/cmake-variables.7.rst
index 36d00dc7d..e134a1a59 100644
--- a/Help/manual/cmake-variables.7.rst
+++ b/Help/manual/cmake-variables.7.rst
@@ -344,10 +344,15 @@ Variables for Languages
    /variable/CMAKE_LANG_CREATE_SHARED_MODULE
    /variable/CMAKE_LANG_CREATE_STATIC_LIBRARY
    /variable/CMAKE_LANG_FLAGS_DEBUG
+   /variable/CMAKE_LANG_FLAGS_DEBUG_INIT
    /variable/CMAKE_LANG_FLAGS_MINSIZEREL
+   /variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT
    /variable/CMAKE_LANG_FLAGS_RELEASE
+   /variable/CMAKE_LANG_FLAGS_RELEASE_INIT
    /variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO
+   /variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT
    /variable/CMAKE_LANG_FLAGS
+   /variable/CMAKE_LANG_FLAGS_INIT
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_DEBUG
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_MINSIZEREL
    /variable/CMAKE_LANG_GHS_KERNEL_FLAGS_RELEASE
diff --git a/Help/release/dev/toolchain-flag-init.rst b/Help/release/dev/toolchain-flag-init.rst
new file mode 100644
index 000000000..251484bc8
--- /dev/null
+++ b/Help/release/dev/toolchain-flag-init.rst
@@ -0,0 +1,7 @@
+toolchain-flag-init
+-------------------
+
+* :variable:`Toolchain files <CMAKE_TOOLCHAIN_FILE>` may now set a
+  :variable:`CMAKE_<LANG>_FLAGS_INIT` variable to initialize the
+  :variable:`CMAKE_<LANG>_FLAGS` cache entry the first time a language is
+  enabled in a build tree.
diff --git a/Help/variable/CMAKE_LANG_FLAGS_DEBUG_INIT.rst b/Help/variable/CMAKE_LANG_FLAGS_DEBUG_INIT.rst
new file mode 100644
index 000000000..dcddb2e26
--- /dev/null
+++ b/Help/variable/CMAKE_LANG_FLAGS_DEBUG_INIT.rst
@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_DEBUG_INIT
+-----------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_DEBUG` cache
+entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.
diff --git a/Help/variable/CMAKE_LANG_FLAGS_INIT.rst b/Help/variable/CMAKE_LANG_FLAGS_INIT.rst
new file mode 100644
index 000000000..1d32cc3fd
--- /dev/null
+++ b/Help/variable/CMAKE_LANG_FLAGS_INIT.rst
@@ -0,0 +1,15 @@
+CMAKE_<LANG>_FLAGS_INIT
+-----------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS` cache entry
+the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also the configuration-specific variables:
+
+* :variable:`CMAKE_<LANG>_FLAGS_DEBUG_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_RELEASE_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_MINSIZEREL_INIT`
+* :variable:`CMAKE_<LANG>_FLAGS_RELWITHDEBINFO_INIT`
diff --git a/Help/variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT.rst b/Help/variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT.rst
new file mode 100644
index 000000000..c0aedf403
--- /dev/null
+++ b/Help/variable/CMAKE_LANG_FLAGS_MINSIZEREL_INIT.rst
@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_MINSIZEREL_INIT
+----------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_MINSIZEREL`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.
diff --git a/Help/variable/CMAKE_LANG_FLAGS_RELEASE_INIT.rst b/Help/variable/CMAKE_LANG_FLAGS_RELEASE_INIT.rst
new file mode 100644
index 000000000..59f92ff6f
--- /dev/null
+++ b/Help/variable/CMAKE_LANG_FLAGS_RELEASE_INIT.rst
@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_RELEASE_INIT
+-------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_RELEASE`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.
diff --git a/Help/variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT.rst b/Help/variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT.rst
new file mode 100644
index 000000000..915f02305
--- /dev/null
+++ b/Help/variable/CMAKE_LANG_FLAGS_RELWITHDEBINFO_INIT.rst
@@ -0,0 +1,10 @@
+CMAKE_<LANG>_FLAGS_RELWITHDEBINFO_INIT
+--------------------------------------
+
+Value used to initialize the :variable:`CMAKE_<LANG>_FLAGS_RELWITHDEBINFO`
+cache entry the first time a build tree is configured for language ``<LANG>``.
+This variable is meant to be set by a :variable:`toolchain file
+<CMAKE_TOOLCHAIN_FILE>`.  CMake may prepend or append content to
+the value based on the environment and target platform.
+
+See also :variable:`CMAKE_<LANG>_FLAGS_INIT`.
diff --git a/Help/variable/CMAKE_USER_MAKE_RULES_OVERRIDE.rst b/Help/variable/CMAKE_USER_MAKE_RULES_OVERRIDE.rst
index 9af0d97d4..622278ee9 100644
--- a/Help/variable/CMAKE_USER_MAKE_RULES_OVERRIDE.rst
+++ b/Help/variable/CMAKE_USER_MAKE_RULES_OVERRIDE.rst
@@ -14,8 +14,10 @@ variables that must be set before CMake builds its first test project
 to check that the compiler for a language works.  It should not be
 used to load a file in cases that a normal :command:`include` will work.  Use
 it only as a last resort for behavior that cannot be achieved any
-other way.  For example, one may set ``CMAKE_C_FLAGS_INIT`` to change the
-default value used to initialize :variable:`CMAKE_C_FLAGS <CMAKE_<LANG>_FLAGS>`
+other way.  For example, one may set the
+:variable:`CMAKE_C_FLAGS_INIT <CMAKE_<LANG>_FLAGS_INIT>` variable
+to change the default value used to initialize the
+:variable:`CMAKE_C_FLAGS <CMAKE_<LANG>_FLAGS>` variable
 before it is cached.  The override file should NOT be used to set anything
 that could be set after languages are enabled, such as variables like
 :variable:`CMAKE_RUNTIME_OUTPUT_DIRECTORY` that affect the placement of
diff --git a/Modules/Compiler/ARMCC.cmake b/Modules/Compiler/ARMCC.cmake
index 3cf628c0d..2ec75c337 100644
--- a/Modules/Compiler/ARMCC.cmake
+++ b/Modules/Compiler/ARMCC.cmake
@@ -20,11 +20,11 @@ set(CMAKE_AR "${CMAKE_ARMCC_AR}" CACHE FILEPATH "The ARMCC archiver" FORCE)
 mark_as_advanced(CMAKE_ARMCC_AR)
 
 macro(__compiler_armcc lang)
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Ospace -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-Otime -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Ospace -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -Otime -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 
   set(CMAKE_${lang}_OUTPUT_EXTENSION ".o")
   set(CMAKE_${lang}_OUTPUT_EXTENSION_REPLACE 1)
diff --git a/Modules/Compiler/Absoft-Fortran.cmake b/Modules/Compiler/Absoft-Fortran.cmake
index 2e1666fbf..da1fc80d4 100644
--- a/Modules/Compiler/Absoft-Fortran.cmake
+++ b/Modules/Compiler/Absoft-Fortran.cmake
@@ -1,8 +1,8 @@
-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 set(CMAKE_Fortran_MODDIR_FLAG "-YMOD_OUT_DIR=")
 set(CMAKE_Fortran_MODPATH_FLAG "-p")
 set(CMAKE_Fortran_VERBOSE_FLAG "-v")
diff --git a/Modules/Compiler/Bruce-C.cmake b/Modules/Compiler/Bruce-C.cmake
index 23676eccb..cfabe6523 100644
--- a/Modules/Compiler/Bruce-C.cmake
+++ b/Modules/Compiler/Bruce-C.cmake
@@ -1,7 +1,7 @@
 # Bruce C Compiler ignores "-g" flag and optimization cannot be
 # enabled here (it is implemented only for 8086 target).
-set (CMAKE_C_FLAGS_INIT "-D__CLASSIC_C__")
-set (CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set (CMAKE_C_FLAGS_MINSIZEREL_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELEASE_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-g -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_INIT " -D__CLASSIC_C__")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -g -DNDEBUG")
diff --git a/Modules/Compiler/G95-Fortran.cmake b/Modules/Compiler/G95-Fortran.cmake
index fd84848b4..2c83fb8fc 100644
--- a/Modules/Compiler/G95-Fortran.cmake
+++ b/Modules/Compiler/G95-Fortran.cmake
@@ -1,8 +1,8 @@
-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-Os")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -Os")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
 set(CMAKE_Fortran_MODDIR_FLAG "-fmod=")
 set(CMAKE_Fortran_VERBOSE_FLAG "-v")
 set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-ffixed-form")
diff --git a/Modules/Compiler/GHS-C.cmake b/Modules/Compiler/GHS-C.cmake
index 3072715de..c30bdecaf 100644
--- a/Modules/Compiler/GHS-C.cmake
+++ b/Modules/Compiler/GHS-C.cmake
@@ -3,11 +3,11 @@ include(Compiler/GHS)
 set(CMAKE_C_VERBOSE_FLAG "-v")
 set(CMAKE_C_OUTPUT_EXTENSION ".o")
 
-set(CMAKE_C_FLAGS_INIT "")
-set(CMAKE_C_FLAGS_DEBUG_INIT "-Odebug -g")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "-Ospace")
-set(CMAKE_C_FLAGS_RELEASE_INIT "-O")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O -g")
+string(APPEND CMAKE_C_FLAGS_INIT " ")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -Odebug -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -Ospace")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -O")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -O -g")
 
 set(CMAKE_C_GHS_KERNEL_FLAGS_DEBUG_INIT "-ldebug ${CMAKE_C_FLAGS_DEBUG_INIT}")
 set(CMAKE_C_GHS_KERNEL_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT}")
diff --git a/Modules/Compiler/GHS-CXX.cmake b/Modules/Compiler/GHS-CXX.cmake
index a51591b2a..b3018a7b6 100644
--- a/Modules/Compiler/GHS-CXX.cmake
+++ b/Modules/Compiler/GHS-CXX.cmake
@@ -3,11 +3,11 @@ include(Compiler/GHS)
 set(CMAKE_CXX_VERBOSE_FLAG "-v")
 set(CMAKE_CXX_OUTPUT_EXTENSION ".o")
 
-set(CMAKE_CXX_FLAGS_INIT "")
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-Odebug -g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-Ospace")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "-O")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-O -g")
+string(APPEND CMAKE_CXX_FLAGS_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -Odebug -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -Ospace")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -O")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " -O -g")
 
 set(CMAKE_CXX_GHS_KERNEL_FLAGS_DEBUG_INIT
   "-ldebug ${CMAKE_CXX_FLAGS_DEBUG_INIT}")
diff --git a/Modules/Compiler/GNU-Fortran.cmake b/Modules/Compiler/GNU-Fortran.cmake
index e9c8a594a..fc848ac42 100644
--- a/Modules/Compiler/GNU-Fortran.cmake
+++ b/Modules/Compiler/GNU-Fortran.cmake
@@ -5,8 +5,8 @@ set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-ffixed-form")
 set(CMAKE_Fortran_FORMAT_FREE_FLAG "-ffree-form")
 
 # No -DNDEBUG for Fortran.
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-Os")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-O3")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -Os")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -O3")
 
 # No -isystem for Fortran because it will not find .mod files.
 unset(CMAKE_INCLUDE_SYSTEM_FLAG_Fortran)
diff --git a/Modules/Compiler/GNU.cmake b/Modules/Compiler/GNU.cmake
index c2d393dc8..34d4eafc2 100644
--- a/Modules/Compiler/GNU.cmake
+++ b/Modules/Compiler/GNU.cmake
@@ -45,11 +45,11 @@ macro(__compiler_gnu lang)
   endif()
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3 -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g -DNDEBUG")
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
   set(CMAKE_${lang}_CREATE_ASSEMBLY_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
   if(NOT APPLE OR NOT CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 4) # work around #4462
diff --git a/Modules/Compiler/Intel.cmake b/Modules/Compiler/Intel.cmake
index ff62804e5..8c3942cfe 100644
--- a/Modules/Compiler/Intel.cmake
+++ b/Modules/Compiler/Intel.cmake
@@ -27,10 +27,10 @@ else()
   macro(__compiler_intel lang)
     set(CMAKE_${lang}_VERBOSE_FLAG "-v")
 
-    set(CMAKE_${lang}_FLAGS_INIT "")
-    set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-    set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os")
-    set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3")
-    set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
+    string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+    string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+    string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os")
+    string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3")
+    string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -g")
   endmacro()
 endif()
diff --git a/Modules/Compiler/PGI-C.cmake b/Modules/Compiler/PGI-C.cmake
index da88c0116..85d6e7e0c 100644
--- a/Modules/Compiler/PGI-C.cmake
+++ b/Modules/Compiler/PGI-C.cmake
@@ -1,4 +1,4 @@
 include(Compiler/PGI)
 __compiler_pgi(C)
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "${CMAKE_C_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
diff --git a/Modules/Compiler/PGI-CXX.cmake b/Modules/Compiler/PGI-CXX.cmake
index 97c9555b1..896e29877 100644
--- a/Modules/Compiler/PGI-CXX.cmake
+++ b/Modules/Compiler/PGI-CXX.cmake
@@ -1,4 +1,4 @@
 include(Compiler/PGI)
 __compiler_pgi(CXX)
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "${CMAKE_CXX_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "${CMAKE_CXX_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -DNDEBUG")
diff --git a/Modules/Compiler/PGI-Fortran.cmake b/Modules/Compiler/PGI-Fortran.cmake
index 2866254fe..3765079a1 100644
--- a/Modules/Compiler/PGI-Fortran.cmake
+++ b/Modules/Compiler/PGI-Fortran.cmake
@@ -4,7 +4,7 @@ __compiler_pgi(Fortran)
 set(CMAKE_Fortran_FORMAT_FIXED_FLAG "-Mnofreeform")
 set(CMAKE_Fortran_FORMAT_FREE_FLAG "-Mfreeform")
 
-set(CMAKE_Fortran_FLAGS_INIT "${CMAKE_Fortran_FLAGS_INIT} -Mpreprocess -Kieee")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "${CMAKE_Fortran_FLAGS_DEBUG_INIT} -Mbounds")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " -Mpreprocess -Kieee")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -Mbounds")
 
 set(CMAKE_Fortran_MODDIR_FLAG "-module ")
diff --git a/Modules/Compiler/PGI.cmake b/Modules/Compiler/PGI.cmake
index 797945f9a..51069c2cf 100644
--- a/Modules/Compiler/PGI.cmake
+++ b/Modules/Compiler/PGI.cmake
@@ -23,11 +23,11 @@ macro(__compiler_pgi lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-v")
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g -O0")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-O2 -s")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-fast -O3 -Mipa=fast")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-O2 -gopt")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g -O0")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -O2 -s")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -fast -O3 -Mipa=fast")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -O2 -gopt")
 
   # Preprocessing and assembly rules.
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
diff --git a/Modules/Compiler/PathScale-C.cmake b/Modules/Compiler/PathScale-C.cmake
index 9db54afa0..94c7d0822 100644
--- a/Modules/Compiler/PathScale-C.cmake
+++ b/Modules/Compiler/PathScale-C.cmake
@@ -1,4 +1,4 @@
 include(Compiler/PathScale)
 __compiler_pathscale(C)
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "${CMAKE_C_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
diff --git a/Modules/Compiler/PathScale-CXX.cmake b/Modules/Compiler/PathScale-CXX.cmake
index 4dd766048..276b81ba5 100644
--- a/Modules/Compiler/PathScale-CXX.cmake
+++ b/Modules/Compiler/PathScale-CXX.cmake
@@ -1,4 +1,4 @@
 include(Compiler/PathScale)
 __compiler_pathscale(CXX)
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "${CMAKE_CXX_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "${CMAKE_CXX_FLAGS_RELEASE_INIT} -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -DNDEBUG")
diff --git a/Modules/Compiler/PathScale.cmake b/Modules/Compiler/PathScale.cmake
index 107f779a9..09ee2ba67 100644
--- a/Modules/Compiler/PathScale.cmake
+++ b/Modules/Compiler/PathScale.cmake
@@ -23,9 +23,9 @@ macro(__compiler_pathscale lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-v")
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g -O0")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-Os")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O3")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-g -O2")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g -O0")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -Os")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O3")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -g -O2")
 endmacro()
diff --git a/Modules/Compiler/SunPro-ASM.cmake b/Modules/Compiler/SunPro-ASM.cmake
index 2fa8b9950..0d67400fe 100644
--- a/Modules/Compiler/SunPro-ASM.cmake
+++ b/Modules/Compiler/SunPro-ASM.cmake
@@ -8,11 +8,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_ASM_FLAG "-R")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_ASM_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_ASM_FLAG "-h")
 
-set(CMAKE_ASM_FLAGS_INIT "")
-set(CMAKE_ASM_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_ASM_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_ASM_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_INIT " ")
+string(APPEND CMAKE_ASM_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_ASM_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 
 # Initialize ASM link type selection flags.  These flags are used when
 # building a shared library, shared module, or executable that links
diff --git a/Modules/Compiler/SunPro-C.cmake b/Modules/Compiler/SunPro-C.cmake
index c4529833d..503684a36 100644
--- a/Modules/Compiler/SunPro-C.cmake
+++ b/Modules/Compiler/SunPro-C.cmake
@@ -7,11 +7,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-R")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_C_FLAG "-h")
 
-set(CMAKE_C_FLAGS_INIT "")
-set(CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_INIT " ")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 
 # Initialize C link type selection flags.  These flags are used when
 # building a shared library, shared module, or executable that links
diff --git a/Modules/Compiler/SunPro-CXX.cmake b/Modules/Compiler/SunPro-CXX.cmake
index b4a5591b4..ce01cddf0 100644
--- a/Modules/Compiler/SunPro-CXX.cmake
+++ b/Modules/Compiler/SunPro-CXX.cmake
@@ -7,11 +7,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_CXX_FLAG "-R")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_CXX_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_CXX_FLAG "-h")
 
-set(CMAKE_CXX_FLAGS_INIT "")
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 
 # Initialize C link type selection flags.  These flags are used when
 # building a shared library, shared module, or executable that links
diff --git a/Modules/Compiler/SunPro-Fortran.cmake b/Modules/Compiler/SunPro-Fortran.cmake
index 610e19176..a0e07d4cb 100644
--- a/Modules/Compiler/SunPro-Fortran.cmake
+++ b/Modules/Compiler/SunPro-Fortran.cmake
@@ -10,11 +10,11 @@ set(CMAKE_SHARED_LIBRARY_RUNTIME_Fortran_FLAG_SEP ":")
 set(CMAKE_SHARED_LIBRARY_SONAME_Fortran_FLAG "-h")
 set(CMAKE_EXECUTABLE_RUNTIME_Fortran_FLAG "-R")
 
-set(CMAKE_Fortran_FLAGS_INIT "")
-set(CMAKE_Fortran_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "-xO2 -xspace -DNDEBUG")
-set(CMAKE_Fortran_FLAGS_RELEASE_INIT "-xO3 -DNDEBUG")
-set(CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "-g -xO2 -DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " ")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " -xO2 -xspace -DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " -xO3 -DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " -g -xO2 -DNDEBUG")
 set(CMAKE_Fortran_MODDIR_FLAG "-moddir=")
 set(CMAKE_Fortran_MODPATH_FLAG "-M")
 
diff --git a/Modules/Compiler/TinyCC-C.cmake b/Modules/Compiler/TinyCC-C.cmake
index f7937acdf..fbd2841e3 100644
--- a/Modules/Compiler/TinyCC-C.cmake
+++ b/Modules/Compiler/TinyCC-C.cmake
@@ -1,8 +1,8 @@
 set(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-shared")
 
 # no optimization in tcc:
-set (CMAKE_C_FLAGS_INIT "")
-set (CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set (CMAKE_C_FLAGS_MINSIZEREL_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELEASE_INIT "-DNDEBUG")
-set (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-g -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_INIT " ")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -g -DNDEBUG")
diff --git a/Modules/Compiler/XL-ASM.cmake b/Modules/Compiler/XL-ASM.cmake
index 212179e34..9177b392b 100644
--- a/Modules/Compiler/XL-ASM.cmake
+++ b/Modules/Compiler/XL-ASM.cmake
@@ -2,11 +2,11 @@ set(CMAKE_ASM_VERBOSE_FLAG "-V")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_ASM_FLAGS_INIT "-qthreaded -qhalt=e -qsourcetype=assembler")
+string(APPEND CMAKE_ASM_FLAGS_INIT " -qthreaded -qhalt=e -qsourcetype=assembler")
 
-set(CMAKE_ASM_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_ASM_FLAGS_RELEASE_INIT "-O -DNDEBUG")
-set(CMAKE_ASM_FLAGS_MINSIZEREL_INIT "-O -DNDEBUG")
-set(CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT "-g -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_ASM_FLAGS_RELEASE_INIT " -O -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_MINSIZEREL_INIT " -O -DNDEBUG")
+string(APPEND CMAKE_ASM_FLAGS_RELWITHDEBINFO_INIT " -g -DNDEBUG")
 
 set(CMAKE_ASM_SOURCE_FILE_EXTENSIONS s )
diff --git a/Modules/Compiler/XL-C.cmake b/Modules/Compiler/XL-C.cmake
index 97dd01789..f976c9912 100644
--- a/Modules/Compiler/XL-C.cmake
+++ b/Modules/Compiler/XL-C.cmake
@@ -1,8 +1,8 @@
 include(Compiler/XL)
 __compiler_xl(C)
-set(CMAKE_C_FLAGS_RELEASE_INIT "${CMAKE_C_FLAGS_RELEASE_INIT} -DNDEBUG")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "${CMAKE_C_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_C_FLAGS_INIT "-qthreaded -qhalt=e")
+string(APPEND CMAKE_C_FLAGS_INIT " -qthreaded -qhalt=e")
diff --git a/Modules/Compiler/XL-CXX.cmake b/Modules/Compiler/XL-CXX.cmake
index 41372c15b..545d65732 100644
--- a/Modules/Compiler/XL-CXX.cmake
+++ b/Modules/Compiler/XL-CXX.cmake
@@ -1,11 +1,11 @@
 include(Compiler/XL)
 __compiler_xl(CXX)
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "${CMAKE_CXX_FLAGS_RELEASE_INIT} -DNDEBUG")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "${CMAKE_CXX_FLAGS_MINSIZEREL_INIT} -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_CXX_FLAGS_INIT "-qthreaded -qhalt=e")
+string(APPEND CMAKE_CXX_FLAGS_INIT " -qthreaded -qhalt=e")
 
 set(CMAKE_CXX_COMPILE_OBJECT
   "<CMAKE_CXX_COMPILER> -+ <DEFINES> <INCLUDES> <FLAGS> -o <OBJECT> -c <SOURCE>")
diff --git a/Modules/Compiler/XL-Fortran.cmake b/Modules/Compiler/XL-Fortran.cmake
index ae9df4e4b..6bab6f69e 100644
--- a/Modules/Compiler/XL-Fortran.cmake
+++ b/Modules/Compiler/XL-Fortran.cmake
@@ -10,7 +10,7 @@ set(CMAKE_Fortran_DEFINE_FLAG "-WF,-D")
 
 # -qthreaded     = Ensures that all optimizations will be thread-safe
 # -qhalt=e       = Halt on error messages (rather than just severe errors)
-set(CMAKE_Fortran_FLAGS_INIT "-qthreaded -qhalt=e")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " -qthreaded -qhalt=e")
 
 # xlf: 1501-214 (W) command option E reserved for future use - ignored
 set(CMAKE_Fortran_CREATE_PREPROCESSED_SOURCE)
diff --git a/Modules/Compiler/XL.cmake b/Modules/Compiler/XL.cmake
index bf4f5541c..1f2b1455e 100644
--- a/Modules/Compiler/XL.cmake
+++ b/Modules/Compiler/XL.cmake
@@ -29,10 +29,10 @@ macro(__compiler_xl lang)
   set(CMAKE_${lang}_VERBOSE_FLAG "-V")
   set(CMAKE_${lang}_COMPILE_OPTIONS_PIC "-qpic")
 
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-g")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-O")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-g")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -g")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -O")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -g")
   set(CMAKE_${lang}_CREATE_PREPROCESSED_SOURCE "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
   set(CMAKE_${lang}_CREATE_ASSEMBLY_SOURCE     "<CMAKE_${lang}_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
 
diff --git a/Modules/Platform/ARTOS-GNU-C.cmake b/Modules/Platform/ARTOS-GNU-C.cmake
index 967d0e7c0..fe8d782e3 100644
--- a/Modules/Platform/ARTOS-GNU-C.cmake
+++ b/Modules/Platform/ARTOS-GNU-C.cmake
@@ -1,9 +1,9 @@
 # Define ARTOS to select proper behaviour and tell preprocessor to accept C++ style comments.
-set(CMAKE_C_FLAGS_INIT "-DARTOS -Xp -+")
+string(APPEND CMAKE_C_FLAGS_INIT " -DARTOS -Xp -+")
 # ac doesn't support -g properly and doesn't support the normal gcc optimization options. Just use the defaults set by ac.
-set(CMAKE_C_FLAGS_DEBUG_INIT "")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "-DNDEBUG")
-set(CMAKE_C_FLAGS_RELEASE_INIT "-DNDEBUG")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " ")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -DNDEBUG")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -DNDEBUG")
 # Most projects expect the stdio functions to be available.
 set(CMAKE_C_STANDARD_LIBRARIES_INIT "stdio.a")
diff --git a/Modules/Platform/Generic-ADSP-C.cmake b/Modules/Platform/Generic-ADSP-C.cmake
index 4b9ed9d07..de1cee298 100644
--- a/Modules/Platform/Generic-ADSP-C.cmake
+++ b/Modules/Platform/Generic-ADSP-C.cmake
@@ -4,10 +4,10 @@ include(Platform/Generic-ADSP-Common)
 
 set(CMAKE_C_OUTPUT_EXTENSION ".doj")
 
-set(CMAKE_C_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_C_FLAGS_MINSIZEREL_INIT "")
-set(CMAKE_C_FLAGS_RELEASE_INIT "")
-set(CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " ")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " ")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " ")
 
 set(CMAKE_C_CREATE_STATIC_LIBRARY
     "<CMAKE_C_COMPILER> -build-lib -proc ${ADSP_PROCESSOR} -si-revision ${ADSP_PROCESSOR_SILICIUM_REVISION} -o <TARGET> <CMAKE_C_LINK_FLAGS> <OBJECTS>")
diff --git a/Modules/Platform/Generic-ADSP-CXX.cmake b/Modules/Platform/Generic-ADSP-CXX.cmake
index 9673aef40..0cde8f2e6 100644
--- a/Modules/Platform/Generic-ADSP-CXX.cmake
+++ b/Modules/Platform/Generic-ADSP-CXX.cmake
@@ -2,10 +2,10 @@ include(Platform/Generic-ADSP-Common)
 
 set(CMAKE_CXX_OUTPUT_EXTENSION ".doj")
 
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " ")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " ")
 
 set(CMAKE_CXX_CREATE_STATIC_LIBRARY
      "<CMAKE_CXX_COMPILER> -build-lib -proc ${ADSP_PROCESSOR} -si-revision ${ADSP_PROCESSOR_SILICIUM_REVISION} -o <TARGET> <CMAKE_CXX_LINK_FLAGS> <OBJECTS>")
diff --git a/Modules/Platform/Generic-SDCC-C.cmake b/Modules/Platform/Generic-SDCC-C.cmake
index a1ca81243..bbefe193e 100644
--- a/Modules/Platform/Generic-SDCC-C.cmake
+++ b/Modules/Platform/Generic-SDCC-C.cmake
@@ -30,7 +30,7 @@ set(CMAKE_AR "${SDCCLIB_EXECUTABLE}" CACHE FILEPATH "The sdcc librarian" FORCE)
 
 # CMAKE_C_FLAGS_INIT and CMAKE_EXE_LINKER_FLAGS_INIT should be set in a CMAKE_SYSTEM_PROCESSOR file
 if(NOT DEFINED CMAKE_C_FLAGS_INIT)
-  set(CMAKE_C_FLAGS_INIT "-mmcs51 --model-small")
+  string(APPEND CMAKE_C_FLAGS_INIT " -mmcs51 --model-small")
 endif()
 
 if(NOT DEFINED CMAKE_EXE_LINKER_FLAGS_INIT)
diff --git a/Modules/Platform/HP-UX-HP-CXX.cmake b/Modules/Platform/HP-UX-HP-CXX.cmake
index 6d90191cb..d37d2b055 100644
--- a/Modules/Platform/HP-UX-HP-CXX.cmake
+++ b/Modules/Platform/HP-UX-HP-CXX.cmake
@@ -8,7 +8,7 @@ set(CMAKE_CXX_CREATE_ASSEMBLY_SOURCE
   "rm -f `basename \"<SOURCE>\" | sed 's/\\.[^./]*$$//'`.o"
   )
 
-set(CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
-set(CMAKE_CXX_FLAGS_MINSIZEREL_INIT "+O3 -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELEASE_INIT "+O2 -DNDEBUG")
-set(CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-g")
+string(APPEND CMAKE_CXX_FLAGS_DEBUG_INIT " -g")
+string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL_INIT " +O3 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELEASE_INIT " +O2 -DNDEBUG")
+string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT " -g")
diff --git a/Modules/Platform/HP-UX-HP.cmake b/Modules/Platform/HP-UX-HP.cmake
index 3935c31c1..398d6fba9 100644
--- a/Modules/Platform/HP-UX-HP.cmake
+++ b/Modules/Platform/HP-UX-HP.cmake
@@ -27,7 +27,7 @@ macro(__hpux_compiler_hp lang)
   set(CMAKE_SHARED_LIBRARY_RUNTIME_${lang}_FLAG_SEP ":")
   set(CMAKE_SHARED_LIBRARY_SONAME_${lang}_FLAG "-Wl,+h")
 
-  set(CMAKE_${lang}_FLAGS_INIT "")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ")
 
   set(CMAKE_${lang}_LINK_FLAGS "-Wl,+s,+nodefaultrpath")
 endmacro()
diff --git a/Modules/Platform/Windows-Embarcadero.cmake b/Modules/Platform/Windows-Embarcadero.cmake
index 102e3a651..8a87db371 100644
--- a/Modules/Platform/Windows-Embarcadero.cmake
+++ b/Modules/Platform/Windows-Embarcadero.cmake
@@ -132,10 +132,10 @@ macro(__embarcadero_language lang)
     )
 
   # Initial configuration flags.
-  set(CMAKE_${lang}_FLAGS_INIT "${_tM}")
-  set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-Od -v")
-  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-O1 -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELEASE_INIT "-O2 -DNDEBUG")
-  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-Od")
+  string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_tM}")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -Od -v")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -O1 -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -O2 -DNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -Od")
   set(CMAKE_${lang}_STANDARD_LIBRARIES_INIT "import32.lib")
 endmacro()
diff --git a/Modules/Platform/Windows-Intel-Fortran.cmake b/Modules/Platform/Windows-Intel-Fortran.cmake
index 1b93db85f..3981a092b 100644
--- a/Modules/Platform/Windows-Intel-Fortran.cmake
+++ b/Modules/Platform/Windows-Intel-Fortran.cmake
@@ -4,8 +4,8 @@ set(_COMPILE_Fortran " /fpp")
 set(CMAKE_Fortran_MODDIR_FLAG "-module:")
 set(CMAKE_Fortran_STANDARD_LIBRARIES_INIT "user32.lib")
 __windows_compiler_intel(Fortran)
-set (CMAKE_Fortran_FLAGS_INIT "/W1 /nologo /fpp /libs:dll /threads")
-set (CMAKE_Fortran_FLAGS_DEBUG_INIT "/Od /debug:full /dbglibs")
-set (CMAKE_Fortran_FLAGS_MINSIZEREL_INIT "/O1 /DNDEBUG")
-set (CMAKE_Fortran_FLAGS_RELEASE_INIT "/O2 /DNDEBUG")
-set (CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT "/O2 /debug:full /DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_INIT " /W1 /nologo /fpp /libs:dll /threads")
+string(APPEND CMAKE_Fortran_FLAGS_DEBUG_INIT " /Od /debug:full /dbglibs")
+string(APPEND CMAKE_Fortran_FLAGS_MINSIZEREL_INIT " /O1 /DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELEASE_INIT " /O2 /DNDEBUG")
+string(APPEND CMAKE_Fortran_FLAGS_RELWITHDEBINFO_INIT " /O2 /debug:full /DNDEBUG")
diff --git a/Modules/Platform/Windows-MSVC.cmake b/Modules/Platform/Windows-MSVC.cmake
index 3fd68024e..b1969a2e4 100644
--- a/Modules/Platform/Windows-MSVC.cmake
+++ b/Modules/Platform/Windows-MSVC.cmake
@@ -303,17 +303,17 @@ macro(__windows_compiler_msvc lang)
     if(CMAKE_VS_PLATFORM_TOOLSET MATCHES "v[0-9]+_clang_.*")
       # note: MSVC 14 2015 Update 1 sets -fno-ms-compatibility by default, but this does not allow one to compile many projects
       # that include MS's own headers. CMake itself is affected project too.
-      set(CMAKE_${lang}_FLAGS_INIT "${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} -fms-extensions -fms-compatibility -D_WINDOWS -Wall${_FLAGS_${lang}}")
-      set(CMAKE_${lang}_FLAGS_DEBUG_INIT "-D_DEBUG /MDd -gline-tables-only -fno-inline -O0 ${_RTC1}")
-      set(CMAKE_${lang}_FLAGS_RELEASE_INIT "/MD -O2 -DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "/MD -gline-tables-only -O2 -fno-inline -DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "/MD -DNDEBUG") # TODO: Add '-Os' once VS generator maps it properly for Clang
+      string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} -fms-extensions -fms-compatibility -D_WINDOWS -Wall${_FLAGS_${lang}}")
+      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -D_DEBUG /MDd -gline-tables-only -fno-inline -O0 ${_RTC1}")
+      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " /MD -O2 -DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " /MD -gline-tables-only -O2 -fno-inline -DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " /MD -DNDEBUG") # TODO: Add '-Os' once VS generator maps it properly for Clang
     else()
-      set(CMAKE_${lang}_FLAGS_INIT "${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} /D_WINDOWS /W3${_FLAGS_${lang}}")
-      set(CMAKE_${lang}_FLAGS_DEBUG_INIT "/D_DEBUG /MDd /Zi /Ob0 /Od ${_RTC1}")
-      set(CMAKE_${lang}_FLAGS_RELEASE_INIT "/MD /O2 /Ob2 /DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "/MD /Zi /O2 /Ob1 /DNDEBUG")
-      set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "/MD /O1 /Ob1 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_INIT " ${_PLATFORM_DEFINES}${_PLATFORM_DEFINES_${lang}} /D_WINDOWS /W3${_FLAGS_${lang}}")
+      string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " /D_DEBUG /MDd /Zi /Ob0 /Od ${_RTC1}")
+      string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " /MD /O2 /Ob2 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " /MD /Zi /O2 /Ob1 /DNDEBUG")
+      string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " /MD /O1 /Ob1 /DNDEBUG")
     endif()
   endif()
   set(CMAKE_${lang}_LINKER_SUPPORTS_PDB ON)
@@ -323,7 +323,7 @@ macro(__windows_compiler_msvc lang)
     set(CMAKE_RC_COMPILER_INIT rc)
   endif()
   if(NOT CMAKE_RC_FLAGS_INIT)
-    set(CMAKE_RC_FLAGS_INIT "${_PLATFORM_DEFINES} ${_PLATFORM_DEFINES_${lang}}")
+    string(APPEND CMAKE_RC_FLAGS_INIT " ${_PLATFORM_DEFINES} ${_PLATFORM_DEFINES_${lang}}")
   endif()
 
   enable_language(RC)
diff --git a/Modules/Platform/Windows-OpenWatcom.cmake b/Modules/Platform/Windows-OpenWatcom.cmake
index 7147600eb..269f9230b 100644
--- a/Modules/Platform/Windows-OpenWatcom.cmake
+++ b/Modules/Platform/Windows-OpenWatcom.cmake
@@ -52,13 +52,13 @@ set(CMAKE_BUILD_TYPE_INIT Debug)
 # single/multi-threaded                 /-bm
 # static/DLL run-time libraries         /-br
 # default is setup for multi-threaded + DLL run-time libraries
-set (CMAKE_C_FLAGS_INIT "-bt=nt -w3 -dWIN32 -br -bm")
-set (CMAKE_CXX_FLAGS_INIT "-bt=nt -xs -w3 -dWIN32 -br -bm")
+string(APPEND CMAKE_C_FLAGS_INIT " -bt=nt -w3 -dWIN32 -br -bm")
+string(APPEND CMAKE_CXX_FLAGS_INIT " -bt=nt -xs -w3 -dWIN32 -br -bm")
 foreach(lang C CXX)
-  set (CMAKE_${lang}_FLAGS_DEBUG_INIT "-d2")
-  set (CMAKE_${lang}_FLAGS_MINSIZEREL_INIT "-s -os -d0 -dNDEBUG")
-  set (CMAKE_${lang}_FLAGS_RELEASE_INIT "-s -ot -d0 -dNDEBUG")
-  set (CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT "-s -ot -d1 -dNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_DEBUG_INIT " -d2")
+  string(APPEND CMAKE_${lang}_FLAGS_MINSIZEREL_INIT " -s -os -d0 -dNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELEASE_INIT " -s -ot -d0 -dNDEBUG")
+  string(APPEND CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT " -s -ot -d1 -dNDEBUG")
 endforeach()
 
 foreach(type CREATE_SHARED_LIBRARY CREATE_SHARED_MODULE LINK_EXECUTABLE)
diff --git a/Tests/RunCMake/ToolchainFile/FlagsInit-stdout.txt b/Tests/RunCMake/ToolchainFile/FlagsInit-stdout.txt
new file mode 100644
index 000000000..e18aa8cd6
--- /dev/null
+++ b/Tests/RunCMake/ToolchainFile/FlagsInit-stdout.txt
@@ -0,0 +1,30 @@
+-- CMAKE_C_FLAGS='[^
+]*-DMY_FLAGS_INIT[^
+]*'
+-- CMAKE_C_FLAGS_DEBUG='[^
+]*-DMY_FLAGS_DEBUG_INIT[^
+]*'
+-- CMAKE_C_FLAGS_RELEASE='[^
+]*-DMY_FLAGS_RELEASE_INIT[^
+]*'
+-- CMAKE_C_FLAGS_MINSIZEREL='[^
+]*-DMY_FLAGS_MINSIZEREL_INIT[^
+]*'
+-- CMAKE_C_FLAGS_RELWITHDEBINFO='[^
+]*-DMY_FLAGS_RELWITHDEBINFO_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS='[^
+]*-DMY_FLAGS_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_DEBUG='[^
+]*-DMY_FLAGS_DEBUG_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_RELEASE='[^
+]*-DMY_FLAGS_RELEASE_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_MINSIZEREL='[^
+]*-DMY_FLAGS_MINSIZEREL_INIT[^
+]*'
+-- CMAKE_CXX_FLAGS_RELWITHDEBINFO='[^
+]*-DMY_FLAGS_RELWITHDEBINFO_INIT[^
+]*'
diff --git a/Tests/RunCMake/ToolchainFile/FlagsInit-toolchain.cmake b/Tests/RunCMake/ToolchainFile/FlagsInit-toolchain.cmake
new file mode 100644
index 000000000..4c794b6a4
--- /dev/null
+++ b/Tests/RunCMake/ToolchainFile/FlagsInit-toolchain.cmake
@@ -0,0 +1,7 @@
+foreach(lang C CXX)
+  set(CMAKE_${lang}_FLAGS_INIT -DMY_FLAGS_INIT)
+  set(CMAKE_${lang}_FLAGS_DEBUG_INIT -DMY_FLAGS_DEBUG_INIT)
+  set(CMAKE_${lang}_FLAGS_RELEASE_INIT -DMY_FLAGS_RELEASE_INIT)
+  set(CMAKE_${lang}_FLAGS_MINSIZEREL_INIT -DMY_FLAGS_MINSIZEREL_INIT)
+  set(CMAKE_${lang}_FLAGS_RELWITHDEBINFO_INIT -DMY_FLAGS_RELWITHDEBINFO_INIT)
+endforeach()
diff --git a/Tests/RunCMake/ToolchainFile/FlagsInit.cmake b/Tests/RunCMake/ToolchainFile/FlagsInit.cmake
new file mode 100644
index 000000000..98873bf8b
--- /dev/null
+++ b/Tests/RunCMake/ToolchainFile/FlagsInit.cmake
@@ -0,0 +1,7 @@
+enable_language(C)
+enable_language(CXX)
+foreach(lang C CXX)
+  foreach(c "" _DEBUG _RELEASE _MINSIZEREL _RELWITHDEBINFO)
+    message(STATUS "CMAKE_${lang}_FLAGS${c}='${CMAKE_${lang}_FLAGS${c}}'")
+  endforeach()
+endforeach()
diff --git a/Tests/RunCMake/ToolchainFile/RunCMakeTest.cmake b/Tests/RunCMake/ToolchainFile/RunCMakeTest.cmake
index 75293e7c5..88c82164f 100644
--- a/Tests/RunCMake/ToolchainFile/RunCMakeTest.cmake
+++ b/Tests/RunCMake/ToolchainFile/RunCMakeTest.cmake
@@ -7,3 +7,4 @@ endfunction()
 
 run_cmake_toolchain(CallEnableLanguage)
 run_cmake_toolchain(CallProject)
+run_cmake_toolchain(FlagsInit)