diff --git a/.changeset/tiny-donuts-draw.md b/.changeset/tiny-donuts-draw.md
new file mode 100644
index 00000000000..be5016d0ab2
--- /dev/null
+++ b/.changeset/tiny-donuts-draw.md
@@ -0,0 +1,5 @@
+---
+'@firebase/functions': patch
+---
+
+Update public `FunctionsErrorCode` type to include "functions/" prefix.
diff --git a/common/api-review/functions.api.md b/common/api-review/functions.api.md
index 8c68b578020..90c26814746 100644
--- a/common/api-review/functions.api.md
+++ b/common/api-review/functions.api.md
@@ -24,7 +24,10 @@ export interface FunctionsError extends FirebaseError {
 }
 
 // @public
-export type FunctionsErrorCode = 'ok' | 'cancelled' | 'unknown' | 'invalid-argument' | 'deadline-exceeded' | 'not-found' | 'already-exists' | 'permission-denied' | 'resource-exhausted' | 'failed-precondition' | 'aborted' | 'out-of-range' | 'unimplemented' | 'internal' | 'unavailable' | 'data-loss' | 'unauthenticated';
+export type FunctionsErrorCode = `functions/${FunctionsErrorCodeCore}`;
+
+// @public
+export type FunctionsErrorCodeCore = 'ok' | 'cancelled' | 'unknown' | 'invalid-argument' | 'deadline-exceeded' | 'not-found' | 'already-exists' | 'permission-denied' | 'resource-exhausted' | 'failed-precondition' | 'aborted' | 'out-of-range' | 'unimplemented' | 'internal' | 'unavailable' | 'data-loss' | 'unauthenticated';
 
 // @public
 export function getFunctions(app?: FirebaseApp, regionOrCustomDomain?: string): Functions;
diff --git a/packages/functions-compat/src/callable.test.ts b/packages/functions-compat/src/callable.test.ts
index cf7c58090fe..b04592efb76 100644
--- a/packages/functions-compat/src/callable.test.ts
+++ b/packages/functions-compat/src/callable.test.ts
@@ -35,9 +35,7 @@ async function expectError(
     await promise;
   } catch (e) {
     failed = true;
-    // Errors coming from callable functions usually have the functions
-    // code in the message since it's thrown inside functions.
-    expect(e.code).to.match(new RegExp(`functions.*/${code}`));
+    expect(e.code).to.equal(code);
     expect(e.message).to.equal(message);
     expect(e.details).to.deep.equal(details);
   }
@@ -106,25 +104,29 @@ describe('Firebase Functions > Call', () => {
   it('missing result', async () => {
     const functions = createTestService(app, region);
     const func = functions.httpsCallable('missingResultTest');
-    await expectError(func(), 'internal', 'Response is missing data field.');
+    await expectError(
+      func(),
+      'functions/internal',
+      'Response is missing data field.'
+    );
   });
 
   it('unhandled error', async () => {
     const functions = createTestService(app, region);
     const func = functions.httpsCallable('unhandledErrorTest');
-    await expectError(func(), 'internal', 'internal');
+    await expectError(func(), 'functions/internal', 'internal');
   });
 
   it('unknown error', async () => {
     const functions = createTestService(app, region);
     const func = functions.httpsCallable('unknownErrorTest');
-    await expectError(func(), 'internal', 'internal');
+    await expectError(func(), 'functions/internal', 'internal');
   });
 
   it('explicit error', async () => {
     const functions = createTestService(app, region);
     const func = functions.httpsCallable('explicitErrorTest');
-    await expectError(func(), 'out-of-range', 'explicit nope', {
+    await expectError(func(), 'functions/out-of-range', 'explicit nope', {
       start: 10,
       end: 20,
       long: 30
@@ -134,12 +136,16 @@ describe('Firebase Functions > Call', () => {
   it('http error', async () => {
     const functions = createTestService(app, region);
     const func = functions.httpsCallable('httpErrorTest');
-    await expectError(func(), 'invalid-argument', 'invalid-argument');
+    await expectError(func(), 'functions/invalid-argument', 'invalid-argument');
   });
 
   it('timeout', async () => {
     const functions = createTestService(app, region);
     const func = functions.httpsCallable('timeoutTest', { timeout: 10 });
-    await expectError(func(), 'deadline-exceeded', 'deadline-exceeded');
+    await expectError(
+      func(),
+      'functions/deadline-exceeded',
+      'deadline-exceeded'
+    );
   });
 });
diff --git a/packages/functions/src/callable.test.ts b/packages/functions/src/callable.test.ts
index eda81d53bdf..1d8ae0cdb31 100644
--- a/packages/functions/src/callable.test.ts
+++ b/packages/functions/src/callable.test.ts
@@ -17,7 +17,7 @@
 import { expect } from 'chai';
 import * as sinon from 'sinon';
 import { FirebaseApp } from '@firebase/app';
-import { FunctionsErrorCode } from './public-types';
+import { FunctionsErrorCodeCore } from './public-types';
 import {
   Provider,
   ComponentContainer,
@@ -44,7 +44,7 @@ export const TEST_PROJECT = require('../../../config/project.json');
 // https://github.com/chaijs/chai/issues/608
 async function expectError(
   promise: Promise<any>,
-  code: FunctionsErrorCode,
+  code: FunctionsErrorCodeCore,
   message: string,
   details?: any
 ): Promise<void> {
diff --git a/packages/functions/src/error.ts b/packages/functions/src/error.ts
index b30abbdfe6a..d6f59fd95d3 100644
--- a/packages/functions/src/error.ts
+++ b/packages/functions/src/error.ts
@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-import { FunctionsErrorCode } from './public-types';
+import { FunctionsErrorCodeCore as FunctionsErrorCode } from './public-types';
 import { decode } from './serializer';
 import { HttpResponseBody } from './service';
 import { FirebaseError } from '@firebase/util';
diff --git a/packages/functions/src/index.ts b/packages/functions/src/index.ts
index 89dc5e49b4a..7318b3e64b7 100644
--- a/packages/functions/src/index.ts
+++ b/packages/functions/src/index.ts
@@ -23,5 +23,6 @@
 import { registerFunctions } from './config';
 
 export * from './api';
+export * from './public-types';
 
 registerFunctions(fetch.bind(self));
diff --git a/packages/functions/src/public-types.ts b/packages/functions/src/public-types.ts
index 675c0133ddb..f1c5d23ccba 100644
--- a/packages/functions/src/public-types.ts
+++ b/packages/functions/src/public-types.ts
@@ -72,6 +72,30 @@ export interface Functions {
   customDomain: string | null;
 }
 
+/**
+ * Functions error code string appended after "functions/" product prefix.
+ * See {@link FunctionsErrorCode} for full documentation of codes.
+ * @public
+ */
+export type FunctionsErrorCodeCore =
+  | 'ok'
+  | 'cancelled'
+  | 'unknown'
+  | 'invalid-argument'
+  | 'deadline-exceeded'
+  | 'not-found'
+  | 'already-exists'
+  | 'permission-denied'
+  | 'resource-exhausted'
+  | 'failed-precondition'
+  | 'aborted'
+  | 'out-of-range'
+  | 'unimplemented'
+  | 'internal'
+  | 'unavailable'
+  | 'data-loss'
+  | 'unauthenticated';
+
 /**
  * The set of Firebase Functions status codes. The codes are the same at the
  * ones exposed by gRPC here:
@@ -112,24 +136,7 @@ export interface Functions {
  *   credentials for the operation.
  * @public
  */
-export type FunctionsErrorCode =
-  | 'ok'
-  | 'cancelled'
-  | 'unknown'
-  | 'invalid-argument'
-  | 'deadline-exceeded'
-  | 'not-found'
-  | 'already-exists'
-  | 'permission-denied'
-  | 'resource-exhausted'
-  | 'failed-precondition'
-  | 'aborted'
-  | 'out-of-range'
-  | 'unimplemented'
-  | 'internal'
-  | 'unavailable'
-  | 'data-loss'
-  | 'unauthenticated';
+export type FunctionsErrorCode = `functions/${FunctionsErrorCodeCore}`;
 
 /**
  * An error returned by the Firebase Functions client SDK.