diff --git a/glib/gmain.c b/glib/gmain.c
index af979c8b8..a9a287d6c 100644
--- a/glib/gmain.c
+++ b/glib/gmain.c
@@ -969,13 +969,17 @@ g_source_iter_next (GSourceIter *iter, GSource **source)
    * GSourceList to be removed from source_lists (if iter->source is
    * the only source in its list, and it is destroyed), so we have to
    * keep it reffed until after we advance iter->current_list, above.
+   *
+   * Also we first have to ref the next source before unreffing the
+   * previous one as unreffing the previous source can potentially
+   * free the next one.
    */
+  if (next_source && iter->may_modify)
+    g_source_ref (next_source);
 
   if (iter->source && iter->may_modify)
     g_source_unref_internal (iter->source, iter->context, TRUE);
   iter->source = next_source;
-  if (iter->source && iter->may_modify)
-    g_source_ref (iter->source);
 
   *source = iter->source;
   return *source != NULL;