diff --git a/src/web-server/routes/browser-routes.ts b/src/web-server/routes/browser-routes.ts
index 2701339f..14d8bdc3 100644
--- a/src/web-server/routes/browser-routes.ts
+++ b/src/web-server/routes/browser-routes.ts
@@ -93,11 +93,13 @@ router.put('/', async (req: Request, res: Response): Promise<void> => {
 
   try {
     const current = getBrowserConfig();
+    const nextClaudeUserDataDir =
+      claude?.userDataDir === undefined ? current.claude.user_data_dir : claude.userDataDir.trim();
     mutateUnifiedConfig((config) => {
       config.browser = {
         claude: {
           enabled: claude?.enabled ?? current.claude.enabled,
-          user_data_dir: claude?.userDataDir?.trim() || current.claude.user_data_dir,
+          user_data_dir: nextClaudeUserDataDir,
           devtools_port: claude?.devtoolsPort ?? current.claude.devtools_port,
         },
         codex: {
diff --git a/tests/unit/web-server/browser-routes.test.ts b/tests/unit/web-server/browser-routes.test.ts
index 17ed127b..bc6e0305 100644
--- a/tests/unit/web-server/browser-routes.test.ts
+++ b/tests/unit/web-server/browser-routes.test.ts
@@ -152,6 +152,49 @@ describe('browser routes', () => {
     });
   });
 
+  it('treats a blank user-data directory as a reset to the recommended path', async () => {
+    const firstResponse = await fetch(`${baseUrl}/api/browser`, {
+      method: 'PUT',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        claude: {
+          enabled: true,
+          userDataDir: '/tmp/ccs-browser-custom',
+          devtoolsPort: 9333,
+        },
+      }),
+    });
+
+    expect(firstResponse.status).toBe(200);
+
+    const resetResponse = await fetch(`${baseUrl}/api/browser`, {
+      method: 'PUT',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        claude: {
+          userDataDir: '   ',
+        },
+      }),
+    });
+
+    expect(resetResponse.status).toBe(200);
+    const payload = await resetResponse.json();
+    expect(payload.browser.config.claude).toMatchObject({
+      enabled: true,
+      userDataDir: join(tempHome, '.ccs', 'browser', 'chrome-user-data'),
+      devtoolsPort: 9333,
+    });
+
+    const config = loadOrCreateUnifiedConfig();
+    expect(config.browser).toMatchObject({
+      claude: {
+        enabled: true,
+        user_data_dir: join(tempHome, '.ccs', 'browser', 'chrome-user-data'),
+        devtools_port: 9333,
+      },
+    });
+  });
+
   it('rejects invalid DevTools ports at the route boundary', async () => {
     const response = await fetch(`${baseUrl}/api/browser`, {
       method: 'PUT',