diff --git a/CMakeLists.txt b/CMakeLists.txt
index a92f018f5..77f4d8624 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -129,7 +129,7 @@ endif()
 
 string(TOLOWER "${CMAKE_BUILD_TYPE}" CMAKE_BUILD_TYPE_LOWER)
 if (CMAKE_BUILD_TYPE_LOWER MATCHES "(release|relwithdebinfo|minsizerel)")
-  add_gcc_compiler_flags("-D_FORTIFY_SOURCE=2")
+  add_gcc_compiler_flags("-U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2")
 endif()
 
 check_c_compiler_flag("-Werror=format-security -Werror=implicit-function-declaration" WERROR_C_AVAILABLE)