Index: includes/theme.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/theme.inc,v
retrieving revision 1.577
diff -u -p -r1.577 theme.inc
--- includes/theme.inc	22 Feb 2010 19:21:34 -0000	1.577
+++ includes/theme.inc	23 Feb 2010 05:40:33 -0000
@@ -885,6 +885,10 @@ function theme($hook, $variables = array
     if (function_exists($info['function'])) {
       $output = $info['function']($variables);
     }
+    else {
+      watchdog('theme', 'Theme function "@function" not found.', array('@function' => $info['function']), WATCHDOG_WARNING);
+      $output = '';
+    }
   }
   else {
     // Default render function and extension.