diff --git a/Modules/CMakeDetermineSystem.cmake b/Modules/CMakeDetermineSystem.cmake
index 7e6a6dd68..c7db715f4 100644
--- a/Modules/CMakeDetermineSystem.cmake
+++ b/Modules/CMakeDetermineSystem.cmake
@@ -60,19 +60,6 @@ ELSE(CMAKE_HOST_UNIX)
   ENDIF(CMAKE_HOST_WIN32)
 ENDIF(CMAKE_HOST_UNIX)
 
-# this is for compatibility
-# with cmake 2.4 these variables were compiled in
-# now that cmake has to separate between host and target platform
-# two sets are needed. For compatibility the old set of variables is here 
-# set to the compiled-in values, so they still work in custom
-# language or compiler modules where they might be used.
-# After that they are reset in CMakeSystemSpecificInformation.cmake
-# and then set according to the current target platform in the Modules/${CMAKE_SYSTEM_NAME}.cmake file
-SET(APPLE  ${CMAKE_HOST_APPLE})
-SET(UNIX   ${CMAKE_HOST_UNIX})
-SET(CYGWIN ${CMAKE_HOST_CYGWIN})
-SET(WIN32  ${CMAKE_HOST_WIN32})
-
 # if a toolchain file is used, the user wants to cross compile.
 # in this case read the toolchain file and keep the CMAKE_HOST_SYSTEM_*
 # variables around so they can be used in CMakeLists.txt. 
diff --git a/Modules/CMakeSystemSpecificInformation.cmake b/Modules/CMakeSystemSpecificInformation.cmake
index c0af01a4c..561f5e31e 100644
--- a/Modules/CMakeSystemSpecificInformation.cmake
+++ b/Modules/CMakeSystemSpecificInformation.cmake
@@ -3,11 +3,11 @@
 # It is included after the compiler has been determined, so
 # we know things like the compiler name and if the compiler is gnu.
 
-# before cmake 2.6 these variables were compiled-in in cmake
-# now they are set in the Modules/${CMAKE_SYSTEM_NAME}.cmake file
-# In order to keep custom language or compiler files working which might use
-# these variables, they are set to the value of the compiled-in variables in
-# CMakeDetermineSystem.cmake and reset here.
+# before cmake 2.6 these variables were set in cmMakefile.cxx. This is still
+# done to keep scripts and custom language and compiler modules working.
+# But they are reset here and set again in the platform files for the target
+# platform, so they can be used for testing the target platform instead
+# of testing the host platform.
 SET(APPLE  )
 SET(UNIX   )
 SET(CYGWIN )
diff --git a/Source/cmMakefile.cxx b/Source/cmMakefile.cxx
index a6dd2e18a..ecfdf8017 100644
--- a/Source/cmMakefile.cxx
+++ b/Source/cmMakefile.cxx
@@ -1911,16 +1911,31 @@ void cmMakefile::RemoveVariablesInString(std::string& source,
  */
 void cmMakefile::AddDefaultDefinitions()
 {
+/* Up to CMake 2.4 here only WIN32, UNIX and APPLE were set.
+  With CMake must separate between target and host platform. In most cases
+  the tests for WIN32, UNIX and APPLE will be for the target system, so an 
+  additional set of variables for the host system is required ->
+  CMAKE_HOST_WIN32, CMAKE_HOST_UNIX, CMAKE_HOST_APPLE.
+  WIN32, UNIX and APPLE are now set in the platform files in 
+  Modules/Platforms/.
+  To keep cmake scripts (-P) and custom language and compiler modules
+  working, these variables are still also set here in this place, but they
+  will be reset in CMakeSystemSpecificInformation.cmake before the platform 
+  files are executed. */
 #if defined(_WIN32) || defined(__CYGWIN__)
+  this->AddDefinition("WIN32", "1");
   this->AddDefinition("CMAKE_HOST_WIN32", "1");
 #else
+  this->AddDefinition("UNIX", "1");
   this->AddDefinition("CMAKE_HOST_UNIX", "1");
 #endif
   // Cygwin is more like unix so enable the unix commands
 #if defined(__CYGWIN__)
+  this->AddDefinition("UNIX", "1");
   this->AddDefinition("CMAKE_HOST_UNIX", "1");
 #endif
 #if defined(__APPLE__)
+  this->AddDefinition("APPLE", "1");
   this->AddDefinition("CMAKE_HOST_APPLE", "1");
 #endif