diff --git a/Help/release/dev/FindFLEX-DEFINES_FILE.rst b/Help/release/dev/FindFLEX-DEFINES_FILE.rst
new file mode 100644
index 000000000..95133aa4a
--- /dev/null
+++ b/Help/release/dev/FindFLEX-DEFINES_FILE.rst
@@ -0,0 +1,6 @@
+FindFLEX-DEFINES_FILE
+---------------------
+
+* The :module:`FindFLEX` module ``FLEX_TARGET`` macro learned a
+  new ``DEFINES_FILE`` option to specify a custom output header
+  to be generated.
diff --git a/Modules/FindFLEX.cmake b/Modules/FindFLEX.cmake
index c837c52c7..ca6649359 100644
--- a/Modules/FindFLEX.cmake
+++ b/Modules/FindFLEX.cmake
@@ -27,13 +27,17 @@
 #
 # ::
 #
-#   FLEX_TARGET(Name FlexInput FlexOutput [COMPILE_FLAGS <string>])
+#   FLEX_TARGET(Name FlexInput FlexOutput
+#               [COMPILE_FLAGS <string>]
+#               [DEFINES_FILE <string>]
+#               )
 #
 # which creates a custom command to generate the <FlexOutput> file from
 # the <FlexInput> file.  If COMPILE_FLAGS option is specified, the next
-# parameter is added to the flex command line.  Name is an alias used to
-# get details of this custom command.  Indeed the macro defines the
-# following variables:
+# parameter is added to the flex command line. If flex is configured to
+# output a header file, the DEFINES_FILE option may be used to specify its
+# name. Name is an alias used to get details of this custom command.
+# Indeed the macro defines the following variables:
 #
 # ::
 #
@@ -41,6 +45,7 @@
 #   FLEX_${Name}_OUTPUTS - the source file generated by the custom rule, an
 #   alias for FlexOutput
 #   FLEX_${Name}_INPUT - the flex source file, an alias for ${FlexInput}
+#   FLEX_${Name}_OUTPUT_HEADER - the header flex output, if any.
 #
 #
 #
@@ -113,6 +118,8 @@ find_path(FLEX_INCLUDE_DIR FlexLexer.h
 
 mark_as_advanced(FL_LIBRARY FLEX_INCLUDE_DIR)
 
+include(${CMAKE_CURRENT_LIST_DIR}/CMakeParseArguments.cmake)
+
 set(FLEX_INCLUDE_DIRS ${FLEX_INCLUDE_DIR})
 set(FLEX_LIBRARIES ${FL_LIBRARY})
 
@@ -145,31 +152,55 @@ if(FLEX_EXECUTABLE)
   #============================================================
   #
   macro(FLEX_TARGET Name Input Output)
-    set(FLEX_TARGET_usage "FLEX_TARGET(<Name> <Input> <Output> [COMPILE_FLAGS <string>]")
-    if(${ARGC} GREATER 3)
-      if(${ARGC} EQUAL 5)
-        if("${ARGV3}" STREQUAL "COMPILE_FLAGS")
-          set(FLEX_EXECUTABLE_opts  "${ARGV4}")
-          separate_arguments(FLEX_EXECUTABLE_opts)
-        else()
-          message(SEND_ERROR ${FLEX_TARGET_usage})
-        endif()
+    set(FLEX_TARGET_outputs "${Output}")
+    set(FLEX_EXECUTABLE_opts "")
+
+    set(FLEX_TARGET_PARAM_OPTIONS)
+    set(FLEX_TARGET_PARAM_ONE_VALUE_KEYWORDS
+      COMPILE_FLAGS
+      DEFINES_FILE
+      )
+    set(FLEX_TARGET_PARAM_MULTI_VALUE_KEYWORDS)
+
+    cmake_parse_arguments(
+      FLEX_TARGET_ARG
+      "${FLEX_TARGET_PARAM_OPTIONS}"
+      "${FLEX_TARGET_PARAM_ONE_VALUE_KEYWORDS}"
+      "${FLEX_TARGET_MULTI_VALUE_KEYWORDS}"
+      ${ARGN}
+      )
+
+    set(FLEX_TARGET_usage "FLEX_TARGET(<Name> <Input> <Output> [COMPILE_FLAGS <string>] [DEFINES_FILE <string>]")
+
+    if(NOT "${FLEX_TARGET_ARG_UNPARSED_ARGUMENTS}" STREQUAL "")
+      message(SEND_ERROR ${FLEX_TARGET_usage})
+    else()
+      if(NOT "${FLEX_TARGET_ARG_COMPILE_FLAGS}" STREQUAL "")
+        set(FLEX_EXECUTABLE_opts "${FLEX_TARGET_ARG_COMPILE_FLAGS}")
+        separate_arguments(FLEX_EXECUTABLE_opts)
+      endif()
+      if(NOT "${FLEX_TARGET_ARG_DEFINES_FILE}" STREQUAL "")
+        list(APPEND FLEX_TARGET_outputs "${FLEX_TARGET_ARG_DEFINES_FILE}")
+        list(APPEND FLEX_EXECUTABLE_opts --header-file=${FLEX_TARGET_ARG_DEFINES_FILE})
+      endif()
+
+      add_custom_command(OUTPUT ${FLEX_TARGET_outputs}
+        COMMAND ${FLEX_EXECUTABLE}
+        ARGS ${FLEX_EXECUTABLE_opts} -o${Output} ${Input}
+        DEPENDS ${Input}
+        COMMENT "[FLEX][${Name}] Building scanner with flex ${FLEX_VERSION}"
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
+
+      set(FLEX_${Name}_DEFINED TRUE)
+      set(FLEX_${Name}_OUTPUTS ${Output})
+      set(FLEX_${Name}_INPUT ${Input})
+      set(FLEX_${Name}_COMPILE_FLAGS ${FLEX_EXECUTABLE_opts})
+      if("${FLEX_TARGET_ARG_DEFINES_FILE}" STREQUAL "")
+        set(FLEX_${Name}_OUTPUT_HEADER "")
       else()
-        message(SEND_ERROR ${FLEX_TARGET_usage})
+        set(FLEX_${Name}_OUTPUT_HEADER ${FLEX_TARGET_ARG_DEFINES_FILE})
       endif()
     endif()
-
-    add_custom_command(OUTPUT ${Output}
-      COMMAND ${FLEX_EXECUTABLE}
-      ARGS ${FLEX_EXECUTABLE_opts} -o${Output} ${Input}
-      DEPENDS ${Input}
-      COMMENT "[FLEX][${Name}] Building scanner with flex ${FLEX_VERSION}"
-      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})
-
-    set(FLEX_${Name}_DEFINED TRUE)
-    set(FLEX_${Name}_OUTPUTS ${Output})
-    set(FLEX_${Name}_INPUT ${Input})
-    set(FLEX_${Name}_COMPILE_FLAGS ${FLEX_EXECUTABLE_opts})
   endmacro()
   #============================================================
 
@@ -181,11 +212,11 @@ if(FLEX_EXECUTABLE)
   macro(ADD_FLEX_BISON_DEPENDENCY FlexTarget BisonTarget)
 
     if(NOT FLEX_${FlexTarget}_OUTPUTS)
-      message(SEND_ERROR "Flex target `${FlexTarget}' does not exists.")
+      message(SEND_ERROR "Flex target `${FlexTarget}' does not exist.")
     endif()
 
     if(NOT BISON_${BisonTarget}_OUTPUT_HEADER)
-      message(SEND_ERROR "Bison target `${BisonTarget}' does not exists.")
+      message(SEND_ERROR "Bison target `${BisonTarget}' does not exist.")
     endif()
 
     set_source_files_properties(${FLEX_${FlexTarget}_OUTPUTS}