diff --git a/src/Symfony/Component/HttpClient/HttpClientTrait.php b/src/Symfony/Component/HttpClient/HttpClientTrait.php
index ab5f3502f7c00..2914ab20b6022 100644
--- a/src/Symfony/Component/HttpClient/HttpClientTrait.php
+++ b/src/Symfony/Component/HttpClient/HttpClientTrait.php
@@ -196,7 +196,7 @@ private static function normalizeHeaders(array $headers): array
         $normalizedHeaders = [];
 
         foreach ($headers as $name => $values) {
-            if (\is_object($values) && method_exists('__toString')) {
+            if (\is_object($values) && method_exists($values, '__toString')) {
                 $values = (string) $values;
             }