diff --git a/packages/twenty-sdk/src/cli/utilities/auth/__tests__/callback-server.test.ts b/packages/twenty-sdk/src/cli/utilities/auth/__tests__/callback-server.test.ts
index 2159793af1..44792fcc57 100644
--- a/packages/twenty-sdk/src/cli/utilities/auth/__tests__/callback-server.test.ts
+++ b/packages/twenty-sdk/src/cli/utilities/auth/__tests__/callback-server.test.ts
@@ -2,14 +2,26 @@ import http from 'node:http';
 
 import { startCallbackServer } from '../callback-server';
 
-const httpGet = (url: string): Promise<{ status: number; body: string }> =>
+const httpGet = (
+  url: string,
+): Promise<{
+  status: number;
+  body: string;
+  headers: http.IncomingHttpHeaders;
+}> =>
   new Promise((resolve, reject) => {
     http
       .get(url, (res) => {
         let body = '';
 
         res.on('data', (chunk: string) => (body += chunk));
-        res.on('end', () => resolve({ status: res.statusCode ?? 0, body }));
+        res.on('end', () =>
+          resolve({
+            status: res.statusCode ?? 0,
+            body,
+            headers: res.headers,
+          }),
+        );
       })
       .on('error', reject);
   });
@@ -44,6 +56,46 @@ describe('startCallbackServer', () => {
     }
   });
 
+  it('should send the success page with an explicit Content-Length (not chunked)', async () => {
+    const server = await startCallbackServer();
+
+    try {
+      const waitPromise = server.waitForCallback();
+
+      const response = await httpGet(
+        `${server.callbackUrl}?code=test-auth-code`,
+      );
+
+      await waitPromise;
+
+      expect(response.status).toBe(200);
+      expect(response.headers['transfer-encoding']).toBeUndefined();
+      expect(response.headers['content-length']).toBe(
+        String(Buffer.byteLength(response.body)),
+      );
+      expect(response.body).toContain('Authentication successful');
+    } finally {
+      server.close();
+    }
+  });
+
+  it('should deliver the full page even when the server is closed right after the callback resolves', async () => {
+    const server = await startCallbackServer();
+
+    const responsePromise = httpGet(
+      `${server.callbackUrl}?code=test-auth-code`,
+    );
+
+    await server.waitForCallback();
+    server.close();
+
+    const response = await responsePromise;
+
+    expect(response.status).toBe(200);
+    expect(response.body).toContain('Authentication successful');
+    expect(response.body).toContain('</html>');
+  });
+
   it('should resolve with error when callback contains an error', async () => {
     const server = await startCallbackServer();
 
diff --git a/packages/twenty-sdk/src/cli/utilities/auth/callback-server.ts b/packages/twenty-sdk/src/cli/utilities/auth/callback-server.ts
index d1b3e8402e..c2e7e69636 100644
--- a/packages/twenty-sdk/src/cli/utilities/auth/callback-server.ts
+++ b/packages/twenty-sdk/src/cli/utilities/auth/callback-server.ts
@@ -195,7 +195,7 @@ export const startCallbackServer = (options?: {
       const url = new URL(req.url ?? '/', `http://127.0.0.1`);
 
       if (url.pathname !== '/callback') {
-        res.writeHead(404);
+        res.writeHead(404, { Connection: 'close' });
         res.end('Not found');
 
         return;
@@ -205,23 +205,28 @@ export const startCallbackServer = (options?: {
       const error = url.searchParams.get('error');
       const isDarkMode = url.searchParams.get('theme') === 'dark';
 
-      const headers = {
+      const result: CallbackResult = code
+        ? { success: true, code }
+        : {
+            success: false,
+            error:
+              error ??
+              url.searchParams.get('error_description') ??
+              'Unknown error',
+          };
+
+      const body = result.success
+        ? successHtml(isDarkMode)
+        : errorHtml(result.error, isDarkMode);
+
+      res.writeHead(200, {
         'Content-Type': 'text/html',
+        'Content-Length': Buffer.byteLength(body),
         Connection: 'close',
-      };
+      });
 
-      if (code) {
-        res.writeHead(200, headers);
-        res.end(successHtml(isDarkMode));
-        callbackResolve({ success: true, code });
-      } else {
-        const errorMessage =
-          error ?? url.searchParams.get('error_description') ?? 'Unknown error';
-
-        res.writeHead(200, headers);
-        res.end(errorHtml(errorMessage, isDarkMode));
-        callbackResolve({ success: false, error: errorMessage });
-      }
+      res.on('close', () => callbackResolve(result));
+      res.end(body);
     });
 
     server.listen(0, '127.0.0.1', () => {
@@ -252,8 +257,8 @@ export const startCallbackServer = (options?: {
         },
         close: () => {
           clearTimeout(timeoutHandle);
-          server.closeAllConnections();
           server.close();
+          server.closeIdleConnections();
         },
       });
     });