diff --git a/glib/gconvert.c b/glib/gconvert.c
index bbc753ee6..4ae0630d5 100644
--- a/glib/gconvert.c
+++ b/glib/gconvert.c
@@ -681,6 +681,8 @@ g_convert_with_fallback (const gchar *str,
   if (!local_error)
     return dest;
 
+  g_assert (dest == NULL);
+
   if (!g_error_matches (local_error, G_CONVERT_ERROR, G_CONVERT_ERROR_ILLEGAL_SEQUENCE))
     {
       g_propagate_error (error, local_error);
diff --git a/glib/gdate.c b/glib/gdate.c
index 68c8689ef..a508c4805 100644
--- a/glib/gdate.c
+++ b/glib/gdate.c
@@ -2725,6 +2725,8 @@ g_date_strftime (gchar       *s,
       g_warning (G_STRLOC "Error converting results of strftime to UTF-8: %s", error->message);
       g_error_free (error);
 
+      g_assert (convbuf == NULL);
+
       s[0] = '\0';
       return 0;
     }