diff --git a/.changeset/tidy-browsers-fail.md b/.changeset/tidy-browsers-fail.md
new file mode 100644
index 0000000000..e1f0da2b3a
--- /dev/null
+++ b/.changeset/tidy-browsers-fail.md
@@ -0,0 +1,5 @@
+---
+'@web/test-runner-core': patch
+---
+
+Mark test sessions as failed when the browser launcher returns errors while stopping the session.
diff --git a/packages/test-runner-core/src/runner/TestScheduler.ts b/packages/test-runner-core/src/runner/TestScheduler.ts
index e13d44b174..5006e64e1b 100644
--- a/packages/test-runner-core/src/runner/TestScheduler.ts
+++ b/packages/test-runner-core/src/runner/TestScheduler.ts
@@ -176,7 +176,7 @@ export class TestScheduler {
           'Timed out stopping the browser page',
           this.config.testsFinishTimeout,
         );
-        updatedSession.errors = [...(updatedSession.errors ?? []), ...(errors ?? [])];
+        sessionErrors.push(...(errors ?? []));
         updatedSession.testCoverage = testCoverage;
       }
     } catch (error) {
diff --git a/packages/test-runner-core/test/src/runner/TestScheduler.test.ts b/packages/test-runner-core/test/src/runner/TestScheduler.test.ts
index dd4b0752b5..3d3240e760 100644
--- a/packages/test-runner-core/test/src/runner/TestScheduler.test.ts
+++ b/packages/test-runner-core/test/src/runner/TestScheduler.test.ts
@@ -223,6 +223,23 @@ describe('TestScheduler', () => {
       assert.equal(finalSession1.errors[0].message, 'mock error');
     });
 
+    it('errors returned while stopping browser mark session as failed', async () => {
+      const [scheduler, sessions, [session1], browser] = createTestFixture('1');
+      browser.stopSession.mock.mockImplementation(() =>
+        Promise.resolve({ errors: [{ message: 'mock error' }] }),
+      );
+      scheduler.schedule(1, [session1]);
+
+      await waitUntilEqual(() => sessions.get(session1.id)!.status, SESSION_STATUS.INITIALIZING);
+
+      sessions.updateStatus({ ...session1, passed: true }, SESSION_STATUS.TEST_FINISHED);
+      await waitUntilEqual(() => sessions.get(session1.id)!.status, SESSION_STATUS.FINISHED);
+      const finalSession1 = sessions.get(session1.id)!;
+      assert.equal(finalSession1.passed, false);
+      assert.equal(finalSession1.errors.length, 1);
+      assert.equal(finalSession1.errors[0].message, 'mock error');
+    });
+
     it('timeout starting the browser marks the session as failed', async () => {
       mockConfig.browserStartTimeout = 2;
       const [scheduler, sessions, [session1], browser] = createTestFixture('1');