diff --git a/tests/e2e/Services/Sites/SitesCustomServerTest.php b/tests/e2e/Services/Sites/SitesCustomServerTest.php
index f1550e3910..f76122c00a 100644
--- a/tests/e2e/Services/Sites/SitesCustomServerTest.php
+++ b/tests/e2e/Services/Sites/SitesCustomServerTest.php
@@ -2697,4 +2697,43 @@ class SitesCustomServerTest extends Scope
 
         $this->cleanupSite($siteId);
     }
+
+    public function testCookieHeader()
+    {
+        $siteId = $this->setupSite([
+            'siteId' => ID::unique(),
+            'name' => 'Astro site',
+            'framework' => 'astro',
+            'adapter' => 'ssr',
+            'buildRuntime' => 'node-22',
+            'outputDirectory' => './dist',
+            'buildCommand' => 'npm run build',
+            'installCommand' => 'npm install',
+            'fallbackFile' => '',
+        ]);
+
+        $this->assertNotEmpty($siteId);
+
+        $domain = $this->setupSiteDomain($siteId);
+
+        $deploymentId = $this->setupDeployment($siteId, [
+            'code' => $this->packageSite('astro'),
+            'activate' => 'true'
+        ]);
+
+        $this->assertNotEmpty($deploymentId);
+
+        $domain = $this->getSiteDomain($siteId);
+        $proxyClient = new Client();
+        $proxyClient->setEndpoint('http://' . $domain);
+
+        $response = $proxyClient->call(Client::METHOD_GET, '/cookies', [
+            'cookie' => 'custom-session-id=abcd123'
+        ]);
+
+        $this->assertEquals(200, $response['headers']['status-code']);
+        $this->assertEquals("abcd123", $response['body']);
+
+        $this->cleanupSite($siteId);
+    }
 }
diff --git a/tests/resources/sites/astro/src/pages/cookies.js b/tests/resources/sites/astro/src/pages/cookies.js
new file mode 100644
index 0000000000..5f5efac833
--- /dev/null
+++ b/tests/resources/sites/astro/src/pages/cookies.js
@@ -0,0 +1,4 @@
+export async function GET(context) {
+  const sessionId = context.cookies.get("custom-session-id")?.value ?? 'Custom session ID missing';
+  return new Response(sessionId);
+}