diff --git a/common/lt_debug.h b/common/lt_debug.h
index 13b08d1..42464b9 100644
--- a/common/lt_debug.h
+++ b/common/lt_debug.h
@@ -13,7 +13,7 @@
 
 extern int debuglevel;
 
-void _lt_debug(int facility, const void *, const char *fmt, ...);
-void _lt_info(int facility, const void *, const char *fmt, ...);
+void _lt_debug(int facility, const void *, const char *fmt, ...) __attribute__ ((format (printf, 3, 4)));
+void _lt_info(int facility, const void *, const char *fmt, ...)  __attribute__ ((format (printf, 3, 4)));
 void lt_debug_init(void);
 #endif