diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 6c69150..b3be6e4 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2488,7 +2489,8 @@ function drupal_valid_test_ua() {
     }
   }
 
-  return FALSE;
+  $test_prefix = FALSE;
+  return $test_prefix;
 }
 
 /**