diff --git a/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php b/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
index 532ce202af..6a0d9aec99 100644
--- a/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
+++ b/src/Symfony/Bridge/PhpUnit/Legacy/SymfonyTestsListenerTrait.php
@@ -326,6 +326,12 @@ class SymfonyTestsListenerTrait
 
             return $h ? $h($type, $msg, $file, $line, $context) : false;
         }
+        // If the message is serialized we need to extract the message. This occurs when the error is triggered by
+        // by the isolated test path in \Symfony\Bridge\PhpUnit\Legacy\SymfonyTestsListenerTrait::endTest().
+        $parsedMsg = @unserialize($msg);
+        if (is_array($parsedMsg)) {
+            $msg = $parsedMsg['deprecation'];
+        }
         if (error_reporting()) {
             $msg = 'Unsilenced deprecation: '.$msg;
         }