diff --git a/CHANGELOG.md b/CHANGELOG.md
index dd05c792..05283d97 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Updated CI to also test on PHP 8.3 #407
 - Updated readme PHP requirement to PHP 7.0+ #407
 - Added dependabot for GitHub Actions #407
+- Cast `$_SERVER['SERVER_PORT']` to integer to prevent adding 80 or 443 port to redirect URL. #403
 
 ## [1.0.0] - 2023-12-13
 
diff --git a/src/OpenIDConnectClient.php b/src/OpenIDConnectClient.php
index 6aa80b17..aea060fc 100644
--- a/src/OpenIDConnectClient.php
+++ b/src/OpenIDConnectClient.php
@@ -696,7 +696,7 @@ public function getRedirectURL(): string
         if (isset($_SERVER['HTTP_X_FORWARDED_PORT'])) {
             $port = (int)$_SERVER['HTTP_X_FORWARDED_PORT'];
         } elseif (isset($_SERVER['SERVER_PORT'])) {
-            $port = $_SERVER['SERVER_PORT'];
+            $port = (int)$_SERVER['SERVER_PORT'];
         } elseif ($protocol === 'https') {
             $port = 443;
         } else {