diff --git a/cmake/compiler_flags.cmake b/cmake/compiler_flags.cmake
index 8c2be6e..388e687 100644
--- a/cmake/compiler_flags.cmake
+++ b/cmake/compiler_flags.cmake
@@ -152,7 +152,8 @@ function (add_cxx_preproc_definition preproc_def)
   string(FIND "${CMAKE_CXX_FLAGS}" "${preproc_def}" PREPROC_DEF_FOUND)
 
   if (${PREPROC_DEF_FOUND} EQUAL -1)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -D${preproc_def}" PARENT_SCOPE)
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -D${preproc_def}" CACHE STRING ""
+        FORCE)
   endif ()
 endfunction ()