diff --git a/CMakeLists.txt b/CMakeLists.txt
index abc0dded..fed8704f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -309,7 +309,7 @@ endif(UNIX)
 
 
 if (CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX)
-	set( CMAKE_C_FLAGS "-Wall -Werror -O4 -fvisibility=hidden " )
+	set( CMAKE_C_FLAGS "-Wall -Werror -O4 -fvisibility=hidden ${CMAKE_C_FLAGS}" )
 endif ()
 
 source_group("Headers Private"  FILES ${HDR_PRIVATE})