diff --git a/src/Provider/AbstractProvider.php b/src/Provider/AbstractProvider.php
index 293a54d6..feba9559 100644
--- a/src/Provider/AbstractProvider.php
+++ b/src/Provider/AbstractProvider.php
@@ -495,7 +495,7 @@ public function getAuthorizationUrl(array $options = [])
      */
     public function authorize(
         array $options = [],
-        callable $redirectHandler = null
+        ?callable $redirectHandler = null
     ) {
         $url = $this->getAuthorizationUrl($options);
         if ($redirectHandler) {