diff --git a/src/ostree/ot-builtin-trivial-httpd.c b/src/ostree/ot-builtin-trivial-httpd.c
index 0300b128..811e8924 100644
--- a/src/ostree/ot-builtin-trivial-httpd.c
+++ b/src/ostree/ot-builtin-trivial-httpd.c
@@ -56,6 +56,9 @@ static GOptionEntry options[] = {
   { NULL }
 };
 
+static void
+httpd_log (OtTrivialHttpd *httpd, const gchar *format, ...) __attribute__ ((format(printf, 2, 3)));
+
 static void
 httpd_log (OtTrivialHttpd *httpd, const gchar *format, ...)
 {