diff --git a/src/Symfony/Component/Debug/DebugClassLoader.php b/src/Symfony/Component/Debug/DebugClassLoader.php
index 53003aa2f5..ac55365294 100644
--- a/src/Symfony/Component/Debug/DebugClassLoader.php
+++ b/src/Symfony/Component/Debug/DebugClassLoader.php
@@ -79,6 +79,7 @@ class DebugClassLoader
     {
         // Ensures we don't hit https://bugs.php.net/42098
         class_exists('Symfony\Component\Debug\ErrorHandler');
+        class_exists('Psr\Log\LogLevel');
 
         if (!is_array($functions = spl_autoload_functions())) {
             return;