diff --git a/Modules/GenerateExportHeader.cmake b/Modules/GenerateExportHeader.cmake
index 735a0d789..e33b927cb 100644
--- a/Modules/GenerateExportHeader.cmake
+++ b/Modules/GenerateExportHeader.cmake
@@ -415,6 +415,7 @@ function(add_compiler_export_flags)
   if(ARGC GREATER 0)
     set(${ARGV0} "${EXTRA_FLAGS}" PARENT_SCOPE)
   else()
-    string(APPEND CMAKE_CXX_FLAGS " ${EXTRA_FLAGS}" PARENT_SCOPE)
+    string(APPEND CMAKE_CXX_FLAGS " ${EXTRA_FLAGS}")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}" PARENT_SCOPE)
   endif()
 endfunction()