diff --git a/modules/common/spec/transfer_http.spec.ts b/modules/common/spec/transfer_http.spec.ts
index d26811a48..93fd563bd 100644
--- a/modules/common/spec/transfer_http.spec.ts
+++ b/modules/common/spec/transfer_http.spec.ts
@@ -36,5 +36,11 @@ describe('TransferHttp', () => {
         new HttpParams().append('b', 'foo').append('a', 'bar'));
       expect(key1).toEqual(key2);
     });
+    it('should encode arrays in url params', () => {
+      const interceptor = new TransferHttpCacheInterceptor(mockAppRef(), mockTransferState());
+      const key = interceptor['makeCacheKey']('GET', 'https://google.com/api',
+        new HttpParams().append('b', 'xyz').append('a', 'foo').append('a', 'bar'));
+      expect(key).toEqual('G.https://google.com/api?a=foo,bar&b=xyz');
+    });
   });
 });
diff --git a/modules/common/src/transfer_http.ts b/modules/common/src/transfer_http.ts
index 479390855..4161c478d 100644
--- a/modules/common/src/transfer_http.ts
+++ b/modules/common/src/transfer_http.ts
@@ -54,7 +54,7 @@ export class TransferHttpCacheInterceptor implements HttpInterceptor {
 
   private makeCacheKey(method: string, url: string, params: HttpParams): StateKey<string> {
     // make the params encoded same as a url so it's easy to identify
-    const encodedParams = params.keys().sort().map(k => `${k}=${params.get(k)}`).join('&');
+    const encodedParams = params.keys().sort().map(k => `${k}=${params.getAll(k)}`).join('&');
     const key = (method === 'GET' ? 'G.' : 'H.') + url + '?' + encodedParams;
 
     return makeStateKey<TransferHttpResponse>(key);