Index: src/gd_errors.h
===================================================================
--- src/gd_errors.h.orig	2013-06-25 11:58:23.000000000 +0200
+++ src/gd_errors.h	2013-12-18 11:47:26.605907096 +0100
@@ -40,7 +40,7 @@
 #define GD_INFO LOG_INFO
 #define GD_DEBUG LOG_DEBUG
 
-void gd_error(const char *format, ...);
-void gd_error_ex(int priority, const char *format, ...);
+void gd_error(const char *format, ...) __attribute__((format(printf, 1, 2)));
+void gd_error_ex(int priority, const char *format, ...) __attribute__((format(printf, 2, 3)));
 
 #endif