diff --git a/udev.h b/udev.h
index fb35cad49a..af1b6bbb8d 100644
--- a/udev.h
+++ b/udev.h
@@ -49,7 +49,8 @@
 /* Binaries that udev calls to do stuff */
 #define MKNOD		"/bin/mknod"
 
-extern int log_message (int level, const char *format, ...);
+extern int log_message (int level, const char *format, ...)
+	__attribute__ ((format (printf, 2, 3)));
 
 
 #endif