diff --git a/cmake/Modules/DefineCompilerFlags.cmake b/cmake/Modules/DefineCompilerFlags.cmake
index 93fed0a9b6..b0d864eeb3 100644
--- a/cmake/Modules/DefineCompilerFlags.cmake
+++ b/cmake/Modules/DefineCompilerFlags.cmake
@@ -16,6 +16,7 @@ if (${CMAKE_C_COMPILER_ID} MATCHES "(GNU|Clang)")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall -Wextra -Wshadow -Wmissing-prototypes -Wdeclaration-after-statement")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wunused -Wfloat-equal -Wpointer-arith -Wwrite-strings -Wformat-security")
     set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wmissing-format-attribute")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wmissing-format-attribute -D_USE_GNU")
 
     set(CSYNC_STRICT ON CACHE BOOL "Strict error checking, enabled -Werror and friends")
     if (CSYNC_STRICT)