diff --git a/includes/theme.inc b/includes/theme.inc
index ff54d6e..bb876f8 100644
--- a/includes/theme.inc
+++ b/includes/theme.inc
@@ -1248,6 +1248,7 @@ function path_to_theme() {
 function drupal_find_theme_functions($cache, $prefixes) {
   $implementations = array();
   $functions = get_defined_functions();
+  $theme_functions = preg_grep('/^(' . implode(')|(', $prefixes) . ')_/', $functions['user']);
 
   foreach ($cache as $hook => $info) {
     foreach ($prefixes as $prefix) {
@@ -1264,7 +1265,7 @@ function drupal_find_theme_functions($cache, $prefixes) {
       // intermediary suggestion.
       $pattern = isset($info['pattern']) ? $info['pattern'] : ($hook . '__');
       if (!isset($info['base hook']) && !empty($pattern)) {
-        $matches = preg_grep('/^' . $prefix . '_' . $pattern . '/', $functions['user']);
+        $matches = preg_grep('/^' . $prefix . '_' . $pattern . '/', $theme_functions);
         if ($matches) {
           foreach ($matches as $match) {
             $new_hook = substr($match, strlen($prefix) + 1);