diff --git a/src/browser/run/runner.test.ts b/src/browser/run/runner.test.ts
index d525667e..b5c8a735 100644
--- a/src/browser/run/runner.test.ts
+++ b/src/browser/run/runner.test.ts
@@ -405,6 +405,14 @@ describe('runBrowserProgram', () => {
     expect(output.result).toBe('undefined');
   });
 
+  it('serializes a program with no explicit return as null', async () => {
+    const output = await run(`
+      await page.getByRole('button', { name: 'Save' }).click();
+    `);
+
+    expect(output.result).toBeNull();
+  });
+
   it('keeps time, memory, output, redaction, and serialization limits', async () => {
     await expect(run('while (true) {}', { timeoutMs: 25 })).rejects.toMatchObject({
       code: 'BROWSER_RUN_TIMEOUT',
diff --git a/src/browser/run/runner.ts b/src/browser/run/runner.ts
index 0cd8eb99..a37ccb96 100644
--- a/src/browser/run/runner.ts
+++ b/src/browser/run/runner.ts
@@ -446,7 +446,7 @@ export async function runBrowserProgram(
             rejectRun = undefined;
           }
           try {
-            const serialized = JSON.stringify(value);
+            const serialized = JSON.stringify(value === undefined ? null : value);
             if (serialized === undefined) throw new TypeError('Result is not JSON serializable.');
             return serialized;
           } catch (cause) {