diff --git a/packages/playwright-core/src/client/harRouter.ts b/packages/playwright-core/src/client/harRouter.ts
index a9ab966b2a574..f3f11f852e37a 100644
--- a/packages/playwright-core/src/client/harRouter.ts
+++ b/packages/playwright-core/src/client/harRouter.ts
@@ -68,9 +68,28 @@ export class HarRouter {
       // test when HAR was recorded but we'd abort it immediately.
       if (response.status === -1)
         return;
+
+
+      // route.fulfill does not support multiple set-cookie headers. We need to merge them into one.
+      const transformedHeaders = response.headers!.reduce((headersMap, { name, value }) => {
+        if (name.toLowerCase() !== 'set-cookie') {
+          // non-set-cookie header gets set as-is
+          headersMap[name] = value;
+        } else {
+          // first set-cookie header gets included as-is
+          if (!headersMap['set-cookie'])
+            headersMap['set-cookie'] = value;
+          else
+            // subsequent set-cookie headers get appended to existing header
+            headersMap['set-cookie'] += `\n${value}`;
+
+        }
+        return headersMap;
+      }, {} as Record<string, string>);
+
       await route.fulfill({
         status: response.status,
-        headers: Object.fromEntries(response.headers!.map(h => [h.name, h.value])),
+        headers: transformedHeaders,
         body: response.body!
       });
       return;
diff --git a/tests/assets/har-fulfill.har b/tests/assets/har-fulfill.har
index 5b679098c878a..39261f5ed371a 100644
--- a/tests/assets/har-fulfill.har
+++ b/tests/assets/har-fulfill.har
@@ -62,6 +62,14 @@
             {
               "name": "content-type",
               "value": "text/html"
+            },
+            {
+              "name": "Set-Cookie",
+              "value": "playwright=works;"
+            },
+            {
+              "name": "Set-Cookie",
+              "value": "with=multiple-set-cookie-headers;"
             }
           ],
           "content": {
diff --git a/tests/library/browsercontext-har.spec.ts b/tests/library/browsercontext-har.spec.ts
index 6e64045902508..f82bd30e87e43 100644
--- a/tests/library/browsercontext-har.spec.ts
+++ b/tests/library/browsercontext-har.spec.ts
@@ -452,6 +452,59 @@ it('should ignore boundary when matching multipart/form-data body', {
   await expect(page2.locator('div')).toHaveText('done');
 });
 
+it('should record single set-cookie headers', {
+  annotation: { type: 'issue', description: 'https://github.com/microsoft/playwright/issues/31495' }
+}, async ({ contextFactory, server }, testInfo) => {
+  server.setRoute('/empty.html', (req, res) => {
+    res.setHeader('Content-Type', 'text/html');
+    res.setHeader('set-cookie', ['first=foo']);
+    res.end();
+  });
+
+  const harPath = testInfo.outputPath('har.zip');
+  const context1 = await contextFactory();
+  await context1.routeFromHAR(harPath, { update: true });
+  const page1 = await context1.newPage();
+  await page1.goto(server.EMPTY_PAGE);
+  const cookie1 = await page1.evaluate(() => document.cookie);
+  expect(cookie1).toBe('first=foo');
+  await context1.close();
+
+  const context2 = await contextFactory();
+  await context2.routeFromHAR(harPath, { notFound: 'abort' });
+  const page2 = await context2.newPage();
+  await page2.goto(server.EMPTY_PAGE);
+  const cookie2 = await page2.evaluate(() => document.cookie);
+  expect(cookie2).toBe('first=foo');
+});
+
+it('should record multiple set-cookie headers', {
+  annotation: { type: 'issue', description: 'https://github.com/microsoft/playwright/issues/31495' }
+}, async ({ contextFactory, server }, testInfo) => {
+  server.setRoute('/empty.html', (req, res) => {
+    res.setHeader('Content-Type', 'text/html');
+    res.setHeader('set-cookie', ['first=foo', 'second=bar']);
+    res.end();
+  });
+
+  const harPath = testInfo.outputPath('har.zip');
+  const context1 = await contextFactory();
+  await context1.routeFromHAR(harPath, { update: true });
+  const page1 = await context1.newPage();
+  await page1.goto(server.EMPTY_PAGE);
+  const cookie1 = await page1.evaluate(() => document.cookie);
+  expect(cookie1.split('; ').sort().join('; ')).toBe('first=foo; second=bar');
+  await context1.close();
+
+  const context2 = await contextFactory();
+  await context2.routeFromHAR(harPath, { notFound: 'abort' });
+  const page2 = await context2.newPage();
+  await page2.goto(server.EMPTY_PAGE);
+  const cookie2 = await page2.evaluate(() => document.cookie);
+  expect(cookie2.split('; ').sort().join('; ')).toBe('first=foo; second=bar');
+});
+
+
 it('should update har.zip for page', async ({ contextFactory, server }, testInfo) => {
   const harPath = testInfo.outputPath('har.zip');
   const context1 = await contextFactory();