diff --git a/glib/gutf8.c b/glib/gutf8.c
index a19f72044..fe0f8ab14 100644
--- a/glib/gutf8.c
+++ b/glib/gutf8.c
@@ -1773,6 +1773,7 @@ g_utf8_strreverse (const gchar *str,
     {
       gchar *m, skip = g_utf8_skip[*(guchar*) p];
       r -= skip;
+      g_assert (r >= result);
       for (m = r; skip; skip--)
         *m++ = *p++;
     }