diff --git a/src/JWT.php b/src/JWT.php
index 30b4cbb7..b5d2bafa 100644
--- a/src/JWT.php
+++ b/src/JWT.php
@@ -192,7 +192,7 @@ public static function encode(
             $header['kid'] = $keyId;
         }
         if (isset($head) && \is_array($head)) {
-            $header = \array_merge($head, $header);
+            $header = \array_merge($header, $head);
         }
         $segments = [];
         $segments[] = static::urlsafeB64Encode((string) static::jsonEncode($header));