diff --git a/lib/assert.js b/lib/assert.js
index ae5ba9043..34a0f7ff2 100644
--- a/lib/assert.js
+++ b/lib/assert.js
@@ -91,6 +91,36 @@ export function isArrayOfClass(object, expectedClass) {
   }
 }
 
+export function isInterface(object, expectedProperties) {
+  const parameter = Object.keys(object).pop();
+  const message = `The '${parameter}' parameter should be an object that has
+    '${expectedProperties}' properties.`;
+
+  for (let property of expectedProperties) {
+    if (!(property in object[parameter])) {
+      throwError(message);
+    }
+  }
+}
+
+export function isArrayOfInterface(object, expectedProperties) {
+  const parameter = Object.keys(object).pop();
+  const message = `The '${parameter}' parameter should be an array containing
+    objects that each have '${expectedProperties}' properties.`;
+
+  if (!Array.isArray(object[parameter])) {
+    throwError(message);
+  }
+
+  for (let item of object[parameter]) {
+    for (let property of expectedProperties) {
+      if (!(property in item)) {
+        throwError(message);
+      }
+    }
+  }
+}
+
 export function isValue(object, expectedValue) {
   const parameter = Object.keys(object).pop();
   const actualValue = object[parameter];
diff --git a/packages/workbox-routing/src/lib/router.js b/packages/workbox-routing/src/lib/router.js
index f599b135d..434367e7e 100644
--- a/packages/workbox-routing/src/lib/router.js
+++ b/packages/workbox-routing/src/lib/router.js
@@ -13,11 +13,12 @@
  limitations under the License.
 */
 
-import Route from './route';
-import {isArrayOfClass, isInstance} from '../../../../lib/assert';
+import {isArrayOfInterface, isInterface} from '../../../../lib/assert';
 import logHelper from '../../../../lib/log-helper.js';
 import normalizeHandler from './normalize-handler';
 
+const ROUTE_INTERFACE = ['match', 'handler', 'method'];
+
 /**
  * The Router takes one or more [Routes]{@link Route} and registers a [`fetch`
  * event listener](https://developer.mozilla.org/en-US/docs/Web/API/FetchEvent)
@@ -220,7 +221,10 @@ class Router {
    * routes to register.
    */
   registerRoutes({routes} = {}) {
-    isArrayOfClass({routes}, Route);
+    // Rather than explicitly checking for Route subclasses, check to ensure
+    // that the object exposes the interface we need.
+    // See https://github.com/GoogleChrome/workbox/issues/385
+    isArrayOfInterface({routes}, ROUTE_INTERFACE);
 
     for (let route of routes) {
       if (!this._routes.has(route.method)) {
@@ -244,7 +248,7 @@ class Router {
    * @param {module:workbox-routing.Route} input.route The route to register.
    */
   registerRoute({route} = {}) {
-    isInstance({route}, Route);
+    isInterface({route}, ROUTE_INTERFACE);
 
     this.registerRoutes({routes: [route]});
   }
@@ -265,7 +269,7 @@ class Router {
    * routes to unregister.
    */
   unregisterRoutes({routes} = {}) {
-    isArrayOfClass({routes}, Route);
+    isArrayOfInterface({routes}, ROUTE_INTERFACE);
 
     for (let route of routes) {
       if (!this._routes.has(route.method)) {
@@ -305,7 +309,7 @@ class Router {
    * @param {module:workbox-routing.Route} input.route The route to unregister.
    */
   unregisterRoute({route} = {}) {
-    isInstance({route}, Route);
+    isInterface({route}, ROUTE_INTERFACE);
 
     this.unregisterRoutes({routes: [route]});
   }
diff --git a/packages/workbox-routing/test/sw/router.js b/packages/workbox-routing/test/sw/router.js
index 5da2dd07d..39419aff6 100644
--- a/packages/workbox-routing/test/sw/router.js
+++ b/packages/workbox-routing/test/sw/router.js
@@ -56,4 +56,47 @@ describe('Test of the Router class', function() {
     expect(router._routes.get('GET')).to.have.members([getRoute1]);
     expect(router._routes.get('PUT')).to.have.members([putRoute1]);
   });
+
+  it(`should fail an assertion when registerRoute() is called with an invalid route`, function() {
+    const router = new workbox.routing.Router();
+    const route = {};
+    try {
+      router.registerRoute({route});
+      throw new Error();
+    } catch(error) {
+      expect(error.name).to.eql('assertion-failed',
+        `The expected assertion-failed error wasn't thrown.`);
+    }
+  });
+
+  it(`should fail an assertion when registerRoutes() is called with one invalid route`, function() {
+    const router = new workbox.routing.Router();
+    const routes = [
+      new workbox.routing.Route({match: MATCH, handler: HANDLER}),
+      {},
+    ];
+
+    try {
+      router.registerRoutes({routes});
+      throw new Error();
+    } catch(error) {
+      expect(error.name).to.eql('assertion-failed',
+        `The expected assertion-failed error wasn't thrown.`);
+    }
+  });
+
+  it(`should succeed when registerRoute() is called with something matching the Route interface`, function() {
+    const router = new workbox.routing.Router();
+    const route = {method: 'GET', match: MATCH, handler: HANDLER};
+    router.registerRoute({route});
+  });
+
+  it(`should succeed when registerRoutes() is called with multiple things matching the Route interface`, function() {
+    const router = new workbox.routing.Router();
+    const routes = [
+      new workbox.routing.Route({match: MATCH, handler: HANDLER}),
+      {method: 'GET', match: MATCH, handler: HANDLER},
+    ];
+    router.registerRoutes({routes});
+  });
 });
diff --git a/packages/workbox-sw/src/lib/router.js b/packages/workbox-sw/src/lib/router.js
index 1f30671cf..1eed85c7f 100644
--- a/packages/workbox-sw/src/lib/router.js
+++ b/packages/workbox-sw/src/lib/router.js
@@ -82,10 +82,12 @@ class Router extends SWRoutingRouter {
    * @param {function|module:workbox-runtime-caching.Handler} handler The
    * handler to use to provide a response if the route matches. The handler
    * argument is ignored if you pass in a Route object, otherwise it's required.
+   * @param {String} [method] Only match requests that use this HTTP method.
+   * Defaults to `'GET'`.
    * @return {module:workbox-routing.Route} The Route object that was
    * registered.
    */
-  registerRoute(capture, handler) {
+  registerRoute(capture, handler, method = 'GET') {
     if (typeof handler === 'function') {
       handler = {
         handle: handler,
@@ -97,9 +99,9 @@ class Router extends SWRoutingRouter {
       if (capture.length === 0) {
         throw ErrorFactory.createError('empty-express-string');
       }
-      route = new ExpressRoute({path: capture, handler});
+      route = new ExpressRoute({path: capture, handler, method});
     } else if (capture instanceof RegExp) {
-      route = new RegExpRoute({regExp: capture, handler});
+      route = new RegExpRoute({regExp: capture, handler, method});
     } else if (capture instanceof Route) {
       route = capture;
     } else {
diff --git a/packages/workbox-sw/test/sw/router.js b/packages/workbox-sw/test/sw/router.js
index d4750b3f2..ce20a1e06 100644
--- a/packages/workbox-sw/test/sw/router.js
+++ b/packages/workbox-sw/test/sw/router.js
@@ -119,4 +119,22 @@ describe('Test workboxSW.router', function() {
     expect(thrownError).to.exist;
     expect(thrownError.name).to.equal('navigation-route-url-string');
   });
+
+  it(`should throw when the method passed in to registerRoute() isn't valid`, function() {
+    const workboxSW = new WorkboxSW();
+    try {
+      workboxSW.router.registerRoute(/123/, () => {}, 'INVALID_METHOD');
+      throw new Error();
+    } catch(error) {
+      expect(error.name).to.eql('assertion-failed',
+        `The expected assertion-failed error wasn't thrown.`);
+    }
+  });
+
+  it(`should use the valid method passed in to registerRoute()`, function() {
+    const workboxSW = new WorkboxSW();
+    const method = 'POST';
+    const route =workboxSW.router.registerRoute(/123/, () => {}, method);
+    expect(route.method).to.eql(method);
+  });
 });