diff --git a/panels.module b/panels.module
index 3fe6ad4..59195f5 100644
--- a/panels.module
+++ b/panels.module
@@ -1202,8 +1202,8 @@ function template_preprocess_panels_pane(&$vars) {
 
   // Add some usable classes based on type/subtype
   ctools_include('cleanstring');
-  $type_class = $content->type ? 'pane-'. ctools_cleanstring($content->type, array('lower case' => TRUE)) : '';
-  $subtype_class = $content->subtype ? 'pane-'. ctools_cleanstring($content->subtype, array('lower case' => TRUE)) : '';
+  $type_class = isset($content->type) ? 'pane-'. ctools_cleanstring($content->type, array('lower case' => TRUE)) : '';
+  $subtype_class = isset($content->subtype) ? 'pane-'. ctools_cleanstring($content->subtype, array('lower case' => TRUE)) : '';
 
   // Sometimes type and subtype are the same. Avoid redundant classes.
   $vars['classes_array'][] = $type_class;