diff --git a/CMakeLists.txt b/CMakeLists.txt
index aae0c0e..1c4cc7d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -202,7 +202,7 @@ configure_file (VERSION.in VERSION)
 if (MINGW)
   set (HARDENING_FLAGS            "-Wformat -Wformat-security -O2 -D_FORTIFY_SOURCE=2")
 else (MINGW)
-  set (HARDENING_FLAGS            "-Wformat -Wformat-security -O2 -D_FORTIFY_SOURCE=2 -fstack-protector -Wl,-z,relro -Wl,-z,now")
+  set (HARDENING_FLAGS            "-Wformat -Wformat-security -O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 -fstack-protector -Wl,-z,relro -Wl,-z,now")
 endif (MINGW)
 
 set (CMAKE_C_FLAGS_DEBUG        "${CMAKE_C_FLAGS_DEBUG} -Werror")