diff --git a/lib/includes/nghttp2/nghttp2.h b/lib/includes/nghttp2/nghttp2.h
index 65077dd5..1c48f013 100644
--- a/lib/includes/nghttp2/nghttp2.h
+++ b/lib/includes/nghttp2/nghttp2.h
@@ -5782,7 +5782,11 @@ nghttp2_stream_get_sum_dependency_weight(nghttp2_stream *stream);
  * ``DEBUGBUILD`` macro defined.
  */
 typedef void (*nghttp2_debug_vprintf_callback)(const char *format,
-                                               va_list args);
+              va_list args)
+#ifdef __GNUC__
+  __attribute__ ((format(printf, 1, 0)))
+#endif
+;
 
 /**
  * @function