diff --git a/packages/core/src/utils/googleQuotaErrors.test.ts b/packages/core/src/utils/googleQuotaErrors.test.ts
index 70800c1be01..c451bfe5ffe 100644
--- a/packages/core/src/utils/googleQuotaErrors.test.ts
+++ b/packages/core/src/utils/googleQuotaErrors.test.ts
@@ -435,6 +435,101 @@ describe('classifyGoogleError', () => {
     expect((result as TerminalQuotaError).reason).toBe('RATE_LIMIT_EXCEEDED');
   });
 
+  it('should return RetryableQuotaError for Cloud Code RATE_LIMIT_EXCEEDED with a zero retry delay', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Rate limit exceeded',
+      details: [
+        {
+          '@type': 'type.googleapis.com/google.rpc.ErrorInfo',
+          reason: 'RATE_LIMIT_EXCEEDED',
+          domain: 'cloudcode-pa.googleapis.com',
+          metadata: {
+            uiMessage: 'true',
+            model: 'gemini-2.5-pro',
+          },
+        },
+        {
+          '@type': 'type.googleapis.com/google.rpc.RetryInfo',
+          retryDelay: '0s',
+        },
+      ],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(new Error());
+    expect(result).toBeInstanceOf(RetryableQuotaError);
+  });
+
+  it('should return RetryableQuotaError for Cloud Code RATE_LIMIT_EXCEEDED with a zero millisecond retry delay', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Rate limit exceeded',
+      details: [
+        {
+          '@type': 'type.googleapis.com/google.rpc.ErrorInfo',
+          reason: 'RATE_LIMIT_EXCEEDED',
+          domain: 'cloudcode-pa.googleapis.com',
+          metadata: {
+            uiMessage: 'true',
+            model: 'gemini-2.5-pro',
+          },
+        },
+        {
+          '@type': 'type.googleapis.com/google.rpc.RetryInfo',
+          retryDelay: '0ms',
+        },
+      ],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(new Error());
+    expect(result).toBeInstanceOf(RetryableQuotaError);
+  });
+
+  it('should return TerminalQuotaError for Cloud Code RATE_LIMIT_EXCEEDED with an unparsable retry delay', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Rate limit exceeded',
+      details: [
+        {
+          '@type': 'type.googleapis.com/google.rpc.ErrorInfo',
+          reason: 'RATE_LIMIT_EXCEEDED',
+          domain: 'cloudcode-pa.googleapis.com',
+          metadata: {
+            uiMessage: 'true',
+            model: 'gemini-2.5-pro',
+          },
+        },
+        {
+          '@type': 'type.googleapis.com/google.rpc.RetryInfo',
+          retryDelay: 'not-a-duration',
+        },
+      ],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(new Error());
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+    expect((result as TerminalQuotaError).reason).toBe('RATE_LIMIT_EXCEEDED');
+  });
+
+  it('should return RetryableQuotaError for a zero retry delay in RetryInfo', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Too many requests',
+      details: [
+        {
+          '@type': 'type.googleapis.com/google.rpc.RetryInfo',
+          retryDelay: '0s',
+        },
+      ],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(new Error());
+    expect(result).toBeInstanceOf(RetryableQuotaError);
+    expect((result as RetryableQuotaError).message).toBe(
+      'Too many requests\nSuggested retry after 0s.',
+    );
+  });
+
   it('should return TerminalQuotaError for Cloud Code QUOTA_EXHAUSTED', () => {
     const apiError: GoogleApiError = {
       code: 429,
diff --git a/packages/core/src/utils/googleQuotaErrors.ts b/packages/core/src/utils/googleQuotaErrors.ts
index dcdbeae1e51..38856138925 100644
--- a/packages/core/src/utils/googleQuotaErrors.ts
+++ b/packages/core/src/utils/googleQuotaErrors.ts
@@ -339,7 +339,9 @@ export function classifyGoogleError(error: unknown): unknown {
 
   if (retryInfo?.retryDelay) {
     const parsedDelay = parseDurationInSeconds(retryInfo.retryDelay);
-    if (parsedDelay) {
+    // `null` means the duration could not be parsed; `0` is a valid delay
+    // meaning "retry immediately", so it must not be discarded.
+    if (parsedDelay !== null) {
       delaySeconds = parsedDelay;
     }
   }
@@ -408,7 +410,7 @@ export function classifyGoogleError(error: unknown): unknown {
   }
 
   // 2. Check for delays in RetryInfo
-  if (retryInfo?.retryDelay && delaySeconds) {
+  if (retryInfo?.retryDelay && delaySeconds !== undefined) {
     if (delaySeconds > MAX_RETRYABLE_DELAY_SECONDS) {
       return new TerminalQuotaError(
         `${googleApiError.message}\nSuggested retry after ${retryInfo.retryDelay}.`,