diff --git a/__tests__/runtime/__snapshots__/integration.test.ts.snap b/__tests__/runtime/__snapshots__/integration.test.ts.snap
index c418bbad..98499d1d 100644
--- a/__tests__/runtime/__snapshots__/integration.test.ts.snap
+++ b/__tests__/runtime/__snapshots__/integration.test.ts.snap
@@ -1,6 +1,23 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`Function integration tests basic-twiml.js should match snapshot 1`] = `
+exports[`with an express app Assets integration tests hello.js should match snapshot 1`] = `
+Object {
+  "body": Object {},
+  "headers": Object {
+    "accept-ranges": "bytes",
+    "cache-control": "public, max-age=0",
+    "connection": "close",
+    "content-type": "application/javascript; charset=UTF-8",
+    "x-powered-by": "Express",
+  },
+  "statusCode": 200,
+  "text": "alert('Hello world!');
+",
+  "type": "application/javascript",
+}
+`;
+
+exports[`with an express app Function integration tests basic-twiml.js should match snapshot 1`] = `
 Object {
   "body": Object {},
   "headers": Object {
diff --git a/__tests__/runtime/integration.test.ts b/__tests__/runtime/integration.test.ts
index 2e804fb6..55c86bd9 100644
--- a/__tests__/runtime/integration.test.ts
+++ b/__tests__/runtime/integration.test.ts
@@ -10,6 +10,7 @@ import { createServer } from '../../src/runtime/server';
 const TEST_DIR = resolve(__dirname, '../../fixtures');
 
 const TEST_FUNCTIONS_DIR = resolve(TEST_DIR, 'functions');
+const TEST_ASSETS_DIR = resolve(TEST_DIR, 'assets');
 const TEST_ENV = {};
 
 const availableFunctions = readdirSync(TEST_FUNCTIONS_DIR).map(
@@ -19,6 +20,11 @@ const availableFunctions = readdirSync(TEST_FUNCTIONS_DIR).map(
     return { name, url, path };
   }
 );
+const availableAssets = readdirSync(TEST_ASSETS_DIR).map((name: string) => {
+  const path = resolve(TEST_ASSETS_DIR, name);
+  const url = `/${name}`;
+  return { name, url, path };
+});
 
 type InternalResponse = request.Response & {
   statusCode: number;
@@ -30,6 +36,7 @@ type InternalResponse = request.Response & {
 function responseToSnapshotJson(response: InternalResponse) {
   let { statusCode, type, body, text, headers } = response;
   delete headers['date'];
+  delete headers['last-modified'];
 
   if (text && text.startsWith('Error')) {
     // stack traces are different in every environment
@@ -48,7 +55,7 @@ function responseToSnapshotJson(response: InternalResponse) {
   };
 }
 
-describe('Function integration tests', () => {
+describe('with an express app', () => {
   let app: Express;
 
   beforeAll(async () => {
@@ -59,15 +66,68 @@ describe('Function integration tests', () => {
     } as StartCliConfig);
   });
 
-  for (const testFnCode of availableFunctions) {
-    test(`${testFnCode.name} should match snapshot`, async () => {
-      const response = await request(app).get(testFnCode.url);
-      if (response.status === 500) {
-        expect(response.text).toMatch(/Error/);
-      } else {
+  describe('Function integration tests', () => {
+    for (const testFnCode of availableFunctions) {
+      test(`${testFnCode.name} should match snapshot`, async () => {
+        const response = await request(app).get(testFnCode.url);
+        if (response.status === 500) {
+          expect(response.text).toMatch(/Error/);
+        } else {
+          const result = responseToSnapshotJson(response as InternalResponse);
+          expect(result).toMatchSnapshot();
+        }
+      });
+    }
+  });
+
+  describe('Assets integration tests', () => {
+    for (const testAsset of availableAssets) {
+      test(`${testAsset.name} should match snapshot`, async () => {
+        const response = await request(app).get(testAsset.url);
         const result = responseToSnapshotJson(response as InternalResponse);
         expect(result).toMatchSnapshot();
-      }
-    });
-  }
+      });
+
+      test(`OPTIONS request to ${testAsset.name} should return CORS headers and no body`, async () => {
+        const response = (await request(app).options(
+          testAsset.url
+        )) as InternalResponse;
+        expect(response.headers['access-control-allow-origin']).toEqual('*');
+        expect(response.headers['access-control-allow-headers']).toEqual(
+          'Accept, Authorization, Content-Type, If-Match, If-Modified-Since, If-None-Match, If-Unmodified-Since'
+        );
+        expect(response.headers['access-control-allow-methods']).toEqual(
+          'GET, POST, OPTIONS'
+        );
+        expect(response.headers['access-control-expose-headers']).toEqual(
+          'ETag'
+        );
+        expect(response.headers['access-control-max-age']).toEqual('86400');
+        expect(response.headers['access-control-allow-credentials']).toEqual(
+          'true'
+        );
+        expect(response.text).toEqual('');
+      });
+
+      test(`GET request to ${testAsset.name} should not return CORS headers`, async () => {
+        const response = (await request(app).get(
+          testAsset.url
+        )) as InternalResponse;
+        expect(response.headers['access-control-allow-origin']).toBeUndefined();
+        expect(
+          response.headers['access-control-allow-headers']
+        ).toBeUndefined();
+        expect(
+          response.headers['access-control-allow-methods']
+        ).toBeUndefined();
+        expect(
+          response.headers['access-control-expose-headers']
+        ).toBeUndefined();
+        expect(response.headers['access-control-max-age']).toBeUndefined();
+        expect(
+          response.headers['access-control-allow-credentials']
+        ).toBeUndefined();
+      });
+    }
+  });
 });
diff --git a/fixtures/assets/hello.js b/fixtures/assets/hello.js
new file mode 100644
index 00000000..1d156df3
--- /dev/null
+++ b/fixtures/assets/hello.js
@@ -0,0 +1 @@
+alert('Hello world!');
diff --git a/src/runtime/server.ts b/src/runtime/server.ts
index 83563421..198d3615 100644
--- a/src/runtime/server.ts
+++ b/src/runtime/server.ts
@@ -177,6 +177,17 @@ export async function createServer(
         if (routeInfo.filePath) {
           if (routeInfo.access === 'private') {
             res.status(403).send('This asset has been marked as private');
+          } else if (req.method === 'OPTIONS') {
+            res.set({
+              'access-control-allow-origin': '*',
+              'access-control-allow-headers':
+                'Accept, Authorization, Content-Type, If-Match, If-Modified-Since, If-None-Match, If-Unmodified-Since',
+              'access-control-allow-methods': 'GET, POST, OPTIONS',
+              'access-control-expose-headers': 'ETag',
+              'access-control-max-age': '86400',
+              'access-control-allow-credentials': true,
+            });
+            res.status(200).end();
           } else {
             res.sendFile(routeInfo.filePath);
           }