diff --git a/packages/ai/src/methods/chrome-adapter.test.ts b/packages/ai/src/methods/chrome-adapter.test.ts
index fbe7ec1a5c5..adb9ae47d87 100644
--- a/packages/ai/src/methods/chrome-adapter.test.ts
+++ b/packages/ai/src/methods/chrome-adapter.test.ts
@@ -109,6 +109,14 @@ describe('ChromeAdapter', () => {
     });
   });
   describe('isAvailable', () => {
+    it('returns false if mode is undefined', async () => {
+      const adapter = new ChromeAdapter();
+      expect(
+        await adapter.isAvailable({
+          contents: []
+        })
+      ).to.be.false;
+    });
     it('returns false if mode is only cloud', async () => {
       const adapter = new ChromeAdapter(undefined, 'only_in_cloud');
       expect(
@@ -239,7 +247,10 @@ describe('ChromeAdapter', () => {
       const createStub = stub(languageModelProvider, 'create').returns(
         downloadPromise
       );
-      const adapter = new ChromeAdapter(languageModelProvider);
+      const adapter = new ChromeAdapter(
+        languageModelProvider,
+        'prefer_on_device'
+      );
       await adapter.isAvailable({
         contents: [{ role: 'user', parts: [{ text: 'hi' }] }]
       });
@@ -260,7 +271,10 @@ describe('ChromeAdapter', () => {
       const createStub = stub(languageModelProvider, 'create').returns(
         downloadPromise
       );
-      const adapter = new ChromeAdapter(languageModelProvider);
+      const adapter = new ChromeAdapter(
+        languageModelProvider,
+        'prefer_on_device'
+      );
       await adapter.isAvailable({
         contents: [{ role: 'user', parts: [{ text: 'hi' }] }]
       });
diff --git a/packages/ai/src/methods/chrome-adapter.ts b/packages/ai/src/methods/chrome-adapter.ts
index d6de108668d..b61ad9b5f09 100644
--- a/packages/ai/src/methods/chrome-adapter.ts
+++ b/packages/ai/src/methods/chrome-adapter.ts
@@ -68,6 +68,12 @@ export class ChromeAdapter {
    * separation of concerns.</p>
    */
   async isAvailable(request: GenerateContentRequest): Promise<boolean> {
+    if (!this.mode) {
+      logger.debug(
+        `On-device inference unavailable because mode is undefined.`
+      );
+      return false;
+    }
     if (this.mode === 'only_in_cloud') {
       logger.debug(
         `On-device inference unavailable because mode is "only_in_cloud".`