diff --git a/CMakeLists.txt b/CMakeLists.txt
index a85088f..9d47f3a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -302,7 +302,7 @@ if (NOT MINGW)
 
 endif (NOT 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")
 set (CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -Werror")