diff --git a/src/log.h b/src/log.h
index f463e93..7158410 100644
--- a/src/log.h
+++ b/src/log.h
@@ -18,7 +18,8 @@ typedef enum {
   log_fatal = 5
 } log_msgtype_t;
 
-void f2b_log_msg(log_msgtype_t l, const char *fmt, ...);
+void f2b_log_msg(log_msgtype_t l, const char *fmt, ...)
+  __attribute__ ((format (printf, 2, 3)));
 void f2b_log_set_level(const char *level);
 void f2b_log_to_file  (const char *path);
 void f2b_log_to_stderr();