diff --git a/src/core/meta-clipboard-manager.c b/src/core/meta-clipboard-manager.c
index 8485f3725..926a91ef4 100644
--- a/src/core/meta-clipboard-manager.c
+++ b/src/core/meta-clipboard-manager.c
@@ -126,7 +126,7 @@ owner_changed_cb (MetaSelection       *selection,
             }
         }
 
-      if (best_idx < 0)
+      if (!best)
         {
           g_list_free_full (mimetypes, g_free);
           return;
@@ -149,6 +149,8 @@ owner_changed_cb (MetaSelection       *selection,
       g_autoptr (GError) error = NULL;
       g_autoptr (MetaSelectionSource) new_source = NULL;
 
+      g_assert (display->saved_clipboard_mimetype != NULL);
+
       /* Old owner is gone, time to take over */
       new_source = meta_selection_source_memory_new (display->saved_clipboard_mimetype,
                                                      display->saved_clipboard,