diff --git a/src/MessageTrait.php b/src/MessageTrait.php
index 7f50b26d..f43dc0d8 100644
--- a/src/MessageTrait.php
+++ b/src/MessageTrait.php
@@ -411,9 +411,11 @@ private function filterHeaderValue($values) : array
     /**
      * Ensure header name and values are valid.
      *
+     * @param string $name
+     *
      * @throws Exception\InvalidArgumentException
      */
-    private function assertHeader(string $name) : void
+    private function assertHeader($name) : void
     {
         HeaderSecurity::assertValidName($name);
     }