diff --git a/CMakeLists.txt b/CMakeLists.txt
index 549833c..a4e7882 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -487,7 +487,7 @@ install (FILES ${CMAKE_CURRENT_BINARY_DIR}/zones.xml
 
 ## Program
 
-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        "${CMAKE_C_FLAGS_DEBUG} -Werror")
 set (CMAKE_C_FLAGS              "${CMAKE_C_FLAGS} ${HARDENING_FLAGS} -Wall")