diff --git a/gio/xdgmime/xdgmime.c b/gio/xdgmime/xdgmime.c
index 2446d3813..9bb93f791 100644
--- a/gio/xdgmime/xdgmime.c
+++ b/gio/xdgmime/xdgmime.c
@@ -531,7 +531,8 @@ xdg_mime_get_mime_type_for_data (const void *data,
 
   if (len == 0)
     {
-      *result_prio = 100;
+      if (result_prio != NULL)
+        *result_prio = 100;
       return XDG_MIME_TYPE_EMPTY;
     }