diff --git a/.changeset/moody-icons-repeat.md b/.changeset/moody-icons-repeat.md
new file mode 100644
index 00000000000..20927db37f3
--- /dev/null
+++ b/.changeset/moody-icons-repeat.md
@@ -0,0 +1,5 @@
+---
+'@firebase/analytics': patch
+---
+
+Correct `id` type in `setUserId`
diff --git a/common/api-review/analytics.api.md b/common/api-review/analytics.api.md
index 856815b4b5d..af301eebfa0 100644
--- a/common/api-review/analytics.api.md
+++ b/common/api-review/analytics.api.md
@@ -421,7 +421,7 @@ export interface SettingsOptions {
 }
 
 // @public
-export function setUserId(analyticsInstance: Analytics, id: string, options?: AnalyticsCallOptions): void;
+export function setUserId(analyticsInstance: Analytics, id: string | null, options?: AnalyticsCallOptions): void;
 
 // @public
 export function setUserProperties(analyticsInstance: Analytics, properties: CustomParams, options?: AnalyticsCallOptions): void;
diff --git a/packages/analytics/src/api.ts b/packages/analytics/src/api.ts
index 423092361d9..3e3119fcb78 100644
--- a/packages/analytics/src/api.ts
+++ b/packages/analytics/src/api.ts
@@ -177,7 +177,7 @@ export function setCurrentScreen(
  */
 export function setUserId(
   analyticsInstance: Analytics,
-  id: string,
+  id: string | null,
   options?: AnalyticsCallOptions
 ): void {
   analyticsInstance = getModularInstance(analyticsInstance);
diff --git a/packages/analytics/src/functions.test.ts b/packages/analytics/src/functions.test.ts
index efce7145ce6..4deca1a9401 100644
--- a/packages/analytics/src/functions.test.ts
+++ b/packages/analytics/src/functions.test.ts
@@ -116,6 +116,18 @@ describe('FirebaseAnalytics methods', () => {
     });
   });
 
+  it('setUserId() with null (user) id calls gtag correctly (instance)', async () => {
+    await setUserId(gtagStub, fakeInitializationPromise, null);
+    expect(gtagStub).to.have.been.calledWith(
+      GtagCommand.CONFIG,
+      fakeMeasurementId,
+      {
+        'user_id': null,
+        update: true
+      }
+    );
+  });
+
   it('setUserId() calls gtag correctly (instance)', async () => {
     await setUserId(gtagStub, fakeInitializationPromise, 'user123');
     expect(gtagStub).to.have.been.calledWith(
@@ -137,6 +149,15 @@ describe('FirebaseAnalytics methods', () => {
     });
   });
 
+  it('setUserId() with null (user) id calls gtag correctly (global)', async () => {
+    await setUserId(gtagStub, fakeInitializationPromise, null, {
+      global: true
+    });
+    expect(gtagStub).to.be.calledWith(GtagCommand.SET, {
+      'user_id': null
+    });
+  });
+
   it('setUserProperties() calls gtag correctly (instance)', async () => {
     await setUserProperties(gtagStub, fakeInitializationPromise, {
       'currency': 'USD',