diff --git a/src/Symfony/Component/ClassLoader/ClassMapGenerator.php b/src/Symfony/Component/ClassLoader/ClassMapGenerator.php
index 5b8ca598de..e9a93e118c 100644
--- a/src/Symfony/Component/ClassLoader/ClassMapGenerator.php
+++ b/src/Symfony/Component/ClassLoader/ClassMapGenerator.php
@@ -11,10 +11,12 @@
 
 namespace Symfony\Component\ClassLoader;
 
-if (PHP_VERSION_ID >= 50400) {
-    define('SYMFONY_TRAIT', T_TRAIT);
-} else {
-    define('SYMFONY_TRAIT', 0);
+if (!defined('SYMFONY_TRAIT')) {
+    if (PHP_VERSION_ID >= 50400) {
+        define('SYMFONY_TRAIT', T_TRAIT);
+    } else {
+        define('SYMFONY_TRAIT', 0);
+    }
 }
 
 /**