diff --git a/plugins/cache/panels_hash_cache.inc b/plugins/cache/panels_hash_cache.inc
index be1ecbc..0d60772 100644
--- a/plugins/cache/panels_hash_cache.inc
+++ b/plugins/cache/panels_hash_cache.inc
@@ -87,7 +87,9 @@ function panels_hash_cache_get_id($conf, $display, $args, $contexts, $pane) {
   if (isset($display->owner) && isset($display->owner->id)) {
     $id .= '-' . $display->owner->id;
   }
-  $id .= '-' . $display->cache_key;
+  if (isset($display->cache_key)) {
+    $id .= '-' . $display->cache_key;
+  }
   
   if ($pane) {
     $id .= '-' . $pane->pid;