diff --git a/src/aria/combobox/combobox.ts b/src/aria/combobox/combobox.ts
index 704a70d457c2..a5bda22d7c71 100644
--- a/src/aria/combobox/combobox.ts
+++ b/src/aria/combobox/combobox.ts
@@ -130,7 +130,7 @@ export class Combobox extends DeferredContentAware implements OnInit {
   constructor() {
     super();
 
-    afterRenderEffect(() => this._pattern.keyboardEventRelayEffect());
+    afterRenderEffect({write: () => this._pattern.keyboardEventRelayEffect()});
     afterRenderEffect(() => this._pattern.closePopupOnBlurEffect());
     afterRenderEffect(() => {
       this.contentVisible.set(this._pattern.isExpanded());
diff --git a/src/aria/combobox/combobox.zone.spec.ts b/src/aria/combobox/combobox.zone.spec.ts
new file mode 100644
index 000000000000..ab603ee12fbe
--- /dev/null
+++ b/src/aria/combobox/combobox.zone.spec.ts
@@ -0,0 +1,100 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import {Component, computed, signal, provideZoneChangeDetection} from '@angular/core';
+import {ComponentFixture, TestBed, fakeAsync, tick} from '@angular/core/testing';
+import {By} from '@angular/platform-browser';
+import {Combobox} from './combobox';
+import {ComboboxPopup} from './combobox-popup';
+import {ComboboxWidget} from './combobox-widget';
+import {Listbox, Option} from '../listbox';
+
+describe('Combobox Zone.js integration', () => {
+  let fixture: ComponentFixture<ComboboxListboxZoneExample>;
+  let inputElement: HTMLInputElement;
+
+  beforeEach(async () => {
+    TestBed.configureTestingModule({
+      providers: [provideZoneChangeDetection()],
+    });
+    fixture = TestBed.createComponent(ComboboxListboxZoneExample);
+    await fixture.whenStable();
+    const inputDebugElement = fixture.debugElement.query(By.directive(Combobox));
+    inputElement = inputDebugElement.nativeElement as HTMLInputElement;
+  });
+
+  const focus = () => {
+    inputElement.dispatchEvent(new FocusEvent('focusin', {bubbles: true}));
+    fixture.detectChanges();
+  };
+
+  const keydown = (key: string) => {
+    focus();
+    inputElement.dispatchEvent(
+      new KeyboardEvent('keydown', {
+        key,
+        bubbles: true,
+      }),
+    );
+    fixture.detectChanges();
+  };
+
+  function getOption(text: string): HTMLElement | null {
+    const options = Array.from(document.querySelectorAll('[ngoption]')) as HTMLElement[];
+    return options.find(option => option.textContent?.trim() === text) || null;
+  }
+
+  it('should relay ArrowDown to the listbox and update active descendant', fakeAsync(() => {
+    // Open the popup (sets active descendant to Alabama via default state)
+    keydown('ArrowDown');
+    tick();
+    fixture.detectChanges();
+
+    // Check if expanded is true
+    expect(inputElement.getAttribute('aria-expanded')).toBe('true');
+    // Active descendant is bound to host:
+    const alabama = getOption('Alabama')!;
+    expect(inputElement.getAttribute('aria-activedescendant')).toBe(alabama.id);
+
+    // Press ArrowDown again to move to Alaska
+    keydown('ArrowDown');
+    tick();
+    fixture.detectChanges();
+
+    const alaska = getOption('Alaska')!;
+    expect(inputElement.getAttribute('aria-activedescendant')).toBe(alaska.id);
+  }));
+});
+
+@Component({
+  template: `
+    <div class="parent">
+      <input
+        ngCombobox
+        #combobox="ngCombobox"
+        [(value)]="searchString"
+        [(expanded)]="popupExpanded"
+        (click)="popupExpanded.set(true)"
+      />
+      <ng-template ngComboboxPopup [combobox]="combobox">
+        <ul ngListbox ngComboboxWidget #listbox="ngListbox" [activeDescendant]="listbox.activeDescendant()" focusMode="activedescendant" selectionMode="explicit">
+          @for (option of options(); track option) {
+            <li ngOption [value]="option">{{option}}</li>
+          }
+        </ul>
+      </ng-template>
+    </div>
+  `,
+  imports: [Combobox, ComboboxPopup, ComboboxWidget, Listbox, Option],
+})
+class ComboboxListboxZoneExample {
+  popupExpanded = signal(false);
+  searchString = signal('');
+  value = signal<string[]>([]);
+  options = computed(() => ['Alabama', 'Alaska', 'Arizona', 'Arkansas']);
+}
diff --git a/src/aria/private/combobox/combobox.ts b/src/aria/private/combobox/combobox.ts
index a119779db3c7..b0833a03268f 100644
--- a/src/aria/private/combobox/combobox.ts
+++ b/src/aria/private/combobox/combobox.ts
@@ -260,7 +260,8 @@ export class ComboboxPattern {
     untracked(() => {
       const popup = this.inputs.popup();
       if (this.isExpanded()) {
-        popup?.controlTarget()?.dispatchEvent(event);
+        const relayedEvent = new KeyboardEvent(event.type, event);
+        popup?.controlTarget()?.dispatchEvent(relayedEvent);
       }
     });
   }