diff --git a/themes/engines/phptemplate/phptemplate.engine b/themes/engines/phptemplate/phptemplate.engine
index 823239633f1..faa4f320f6e 100644
--- a/themes/engines/phptemplate/phptemplate.engine
+++ b/themes/engines/phptemplate/phptemplate.engine
@@ -63,7 +63,7 @@ function _phptemplate_callback($hook, $variables = array(), $suggestions = array
     $variables = array_merge($variables, call_user_func($variables_function, $hook, $variables));
   }
 
-  if (is_array($variables['template_files'])) {
+  if (isset($variables['template_files'])) {
     $suggestions = array_merge($suggestions, $variables['template_files']);
   }