diff --git a/src/common.c b/src/common.c
index 389120c..5e4b130 100644
--- a/src/common.c
+++ b/src/common.c
@@ -1390,7 +1390,8 @@ join_str_vector (const struct str_vector *v, char delimiter)
 	return str_steal (&result);
 }
 
-ATTRIBUTE_PRINTF (1, 2)
+static char *xstrdup_printf (const char *, ...) ATTRIBUTE_PRINTF (1, 2);
+
 static char *
 xstrdup_printf (const char *format, ...)
 {