diff --git a/CHANGELOG.md b/CHANGELOG.md
index b83e996..60702cc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## NOT RELEASED
 
+### Added
+
+- AWS api-change: Added `ap-southeast-5` region
+
 ### Changed
 
 - Enable compiler optimization for the `sprintf` function.
diff --git a/composer.json b/composer.json
index d90f6d9..16d4d1c 100644
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.5-dev"
+            "dev-master": "2.6-dev"
         }
     }
 }
diff --git a/src/LambdaClient.php b/src/LambdaClient.php
index eeb7663..318245f 100644
--- a/src/LambdaClient.php
+++ b/src/LambdaClient.php
@@ -566,6 +566,7 @@ protected function getEndpointMetadata(?string $region): array
             case 'ap-southeast-2':
             case 'ap-southeast-3':
             case 'ap-southeast-4':
+            case 'ap-southeast-5':
             case 'ca-central-1':
             case 'ca-west-1':
             case 'eu-central-1':