diff --git a/src/Symfony/Bundle/WebServerBundle/Command/ServerLogCommand.php b/src/Symfony/Bundle/WebServerBundle/Command/ServerLogCommand.php
index 5cef9e36d0..7a6b865b27 100644
--- a/src/Symfony/Bundle/WebServerBundle/Command/ServerLogCommand.php
+++ b/src/Symfony/Bundle/WebServerBundle/Command/ServerLogCommand.php
@@ -37,7 +37,7 @@ class ServerLogCommand extends Command
         }
 
         // based on a symfony/symfony package, it crashes due a missing FormatterInterface from monolog/monolog
-        if (!class_exists(FormatterInterface::class)) {
+        if (!interface_exists(FormatterInterface::class)) {
             return false;
         }