diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js
index fd76440..e0854f0 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface.js
@@ -135,6 +135,42 @@
   const ANONYMIZED_REVISION_BASE_URL = ANONYMIZED_CHANGE_BASE_URL +
       '/revisions/*';
 
+  /**
+   * Wrapper around Map for caching server responses. Site-based so that
+   * changes to CANONICAL_PATH will result in a different cache going into
+   * effect.
+   */
+  class SiteBasedCache {
+    constructor() {
+      // Container of per-canonical-path caches.
+      this._data = new Map();
+    }
+
+    // Returns the cache for the current canonical path.
+    _cache() {
+      if (!this._data.has(window.CANONICAL_PATH)) {
+        this._data.set(window.CANONICAL_PATH, new Map());
+      }
+      return this._data.get(window.CANONICAL_PATH);
+    }
+
+    has(key) {
+      return this._cache().has(key);
+    }
+
+    get(key) {
+      return this._cache().get(key);
+    }
+
+    set(key, value) {
+      this._cache().set(key, value);
+    }
+
+    delete(key) {
+      this._cache().delete(key);
+    }
+  }
+
   Polymer({
     is: 'gr-rest-api-interface',
 
@@ -171,7 +207,7 @@
     properties: {
       _cache: {
         type: Object,
-        value: {}, // Intentional to share the object across instances.
+        value: new SiteBasedCache(), // Shared across instances.
       },
       _credentialCheck: {
         type: Object,
@@ -268,7 +304,7 @@
         }
         return res;
       }).catch(err => {
-        const isLoggedIn = !!this._cache['/accounts/self/detail'];
+        const isLoggedIn = !!this._cache.get('/accounts/self/detail');
         if (isLoggedIn && err && err.message === FAILED_TO_FETCH_ERROR) {
           this.checkCredentials();
           return;
@@ -784,7 +820,7 @@
      */
     saveDiffPreferences(prefs, opt_errFn) {
       // Invalidate the cache.
-      this._cache['/accounts/self/preferences.diff'] = undefined;
+      this._cache.delete('/accounts/self/preferences.diff');
       return this._send({
         method: 'PUT',
         url: '/accounts/self/preferences.diff',
@@ -800,7 +836,7 @@
      */
     saveEditPreferences(prefs, opt_errFn) {
       // Invalidate the cache.
-      this._cache['/accounts/self/preferences.edit'] = undefined;
+      this._cache.delete('/accounts/self/preferences.edit');
       return this._send({
         method: 'PUT',
         url: '/accounts/self/preferences.edit',
@@ -816,7 +852,7 @@
         reportUrlAsIs: true,
         errFn: resp => {
           if (!resp || resp.status === 403) {
-            this._cache['/accounts/self/detail'] = null;
+            this._cache.delete('/accounts/self/detail');
           }
         },
       });
@@ -828,7 +864,7 @@
         reportUrlAsIs: true,
         errFn: resp => {
           if (!resp || resp.status === 403) {
-            this._cache['/accounts/self/avatar.change.url'] = null;
+            this._cache.delete('/accounts/self/avatar.change.url');
           }
         },
       });
@@ -910,7 +946,7 @@
       return this._send(req).then(() => {
         // If result of getAccountEmails is in cache, update it in the cache
         // so we don't have to invalidate it.
-        const cachedEmails = this._cache['/accounts/self/emails'];
+        const cachedEmails = this._cache.get('/accounts/self/emails');
         if (cachedEmails) {
           const emails = cachedEmails.map(entry => {
             if (entry.email === email) {
@@ -919,7 +955,7 @@
               return {email};
             }
           });
-          this._cache['/accounts/self/emails'] = emails;
+          this._cache.set('/accounts/self/emails', emails);
         }
       });
     },
@@ -930,11 +966,11 @@
     _updateCachedAccount(obj) {
       // If result of getAccount is in cache, update it in the cache
       // so we don't have to invalidate it.
-      const cachedAccount = this._cache['/accounts/self/detail'];
+      const cachedAccount = this._cache.get('/accounts/self/detail');
       if (cachedAccount) {
         // Replace object in cache with new object to force UI updates.
-        this._cache['/accounts/self/detail'] =
-            Object.assign({}, cachedAccount, obj);
+        this._cache.set('/accounts/self/detail',
+            Object.assign({}, cachedAccount, obj));
       }
     },
 
@@ -1064,14 +1100,14 @@
         if (!res) { return; }
         if (res.status === 403) {
           this.fire('auth-error');
-          this._cache['/accounts/self/detail'] = null;
+          this._cache.delete('/accounts/self/detail');
         } else if (res.ok) {
           return this.getResponseObject(res);
         }
       }).then(res => {
         this._credentialCheck.checking = false;
         if (res) {
-          this._cache['/accounts/self/detail'] = res;
+          this._cache.delete('/accounts/self/detail');
         }
         return res;
       }).catch(err => {
@@ -1154,13 +1190,13 @@
         return this._sharedFetchPromises[req.url];
       }
       // TODO(andybons): Periodic cache invalidation.
-      if (this._cache[req.url] !== undefined) {
-        return Promise.resolve(this._cache[req.url]);
+      if (this._cache.has(req.url)) {
+        return Promise.resolve(this._cache.get(req.url));
       }
       this._sharedFetchPromises[req.url] = this._fetchJSON(req)
           .then(response => {
             if (response !== undefined) {
-              this._cache[req.url] = response;
+              this._cache.set(req.url, response);
             }
             this._sharedFetchPromises[req.url] = undefined;
             return response;
diff --git a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.html b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.html
index d9656e4..8161c35 100644
--- a/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-rest-api-interface_test.html
@@ -38,11 +38,15 @@
   suite('gr-rest-api-interface tests', () => {
     let element;
     let sandbox;
+    let ctr = 0;
 
     setup(() => {
+      // Modify CANONICAL_PATH to effectively reset cache.
+      ctr += 1;
+      window.CANONICAL_PATH = `test${ctr}`;
+
       sandbox = sinon.sandbox.create();
       element = fixture('basic');
-      element._cache = {};
       element._projectLookup = {};
       const testJSON = ')]}\'\n{"hello": "bonjour"}';
       sandbox.stub(window, 'fetch').returns(Promise.resolve({
@@ -85,7 +89,7 @@
 
     test('cached promise', done => {
       const promise = Promise.reject('foo');
-      element._cache['/foo'] = promise;
+      element._cache.set('/foo', promise);
       element._fetchSharedCacheURL({url: '/foo'}).catch(p => {
         assert.equal(p, 'foo');
         done();
@@ -98,19 +102,20 @@
         gr: 'guten tag',
         noval: null,
       });
-      assert.equal(url, '/path/?sp=hola&gr=guten%20tag&noval');
+      assert.equal(url,
+          window.CANONICAL_PATH + '/path/?sp=hola&gr=guten%20tag&noval');
 
       url = element._urlWithParams('/path/', {
         sp: 'hola',
         en: ['hey', 'hi'],
       });
-      assert.equal(url, '/path/?sp=hola&en=hey&en=hi');
+      assert.equal(url, window.CANONICAL_PATH + '/path/?sp=hola&en=hey&en=hi');
 
       // Order must be maintained with array params.
       url = element._urlWithParams('/path/', {
         l: ['c', 'b', 'a'],
       });
-      assert.equal(url, '/path/?l=c&l=b&l=a');
+      assert.equal(url, window.CANONICAL_PATH + '/path/?l=c&l=b&l=a');
     });
 
     test('request callbacks can be canceled', done => {
@@ -441,7 +446,7 @@
           Promise.reject({message: 'Failed to fetch'}));
       window.fetch.onSecondCall().returns(Promise.resolve(fakeAuthResponse));
       // Emulate logged in.
-      element._cache['/accounts/self/detail'] = {};
+      element._cache.set('/accounts/self/detail', {});
       const serverErrorStub = sandbox.stub();
       element.addEventListener('server-error', serverErrorStub);
       const authErrorStub = sandbox.stub();
@@ -450,7 +455,7 @@
         flush(() => {
           assert.isTrue(authErrorStub.called);
           assert.isFalse(serverErrorStub.called);
-          assert.isNull(element._cache['/accounts/self/detail']);
+          assert.isFalse(element._cache.has('/accounts/self/detail'));
           done();
         });
       });
@@ -471,7 +476,7 @@
       ];
       window.fetch.restore();
       sandbox.stub(window, 'fetch', url => {
-        if (url === '/accounts/self/detail') {
+        if (url === window.CANONICAL_PATH + '/accounts/self/detail') {
           return Promise.resolve(responses.shift());
         }
       });
@@ -487,7 +492,7 @@
 
     test('checkCredentials promise rejection', () => {
       window.fetch.restore();
-      element._cache['/accounts/self/detail'] = true;
+      element._cache.set('/accounts/self/detail', true);
       sandbox.spy(element, 'checkCredentials');
       sandbox.stub(window, 'fetch', url => {
         return Promise.reject({message: 'Failed to fetch'});
@@ -515,10 +520,10 @@
     test('saveDiffPreferences invalidates cache line', () => {
       const cacheKey = '/accounts/self/preferences.diff';
       sandbox.stub(element, '_send');
-      element._cache[cacheKey] = {tab_size: 4};
+      element._cache.set(cacheKey, {tab_size: 4});
       element.saveDiffPreferences({tab_size: 8});
       assert.isTrue(element._send.called);
-      assert.notOk(element._cache[cacheKey]);
+      assert.isFalse(element._cache.has(cacheKey));
     });
 
     test('getAccount when resp is null does not add anything to the cache',
@@ -529,11 +534,11 @@
 
           element.getAccount().then(() => {
             assert.isTrue(element._fetchSharedCacheURL.called);
-            assert.isNull(element._cache[cacheKey]);
+            assert.isFalse(element._cache.has(cacheKey));
             done();
           });
 
-          element._cache[cacheKey] = 'fake cache';
+          element._cache.set(cacheKey, 'fake cache');
           stub.lastCall.args[0].errFn();
         });
 
@@ -545,10 +550,10 @@
 
           element.getAccount().then(() => {
             assert.isTrue(element._fetchSharedCacheURL.called);
-            assert.isNull(element._cache[cacheKey]);
+            assert.isFalse(element._cache.has(cacheKey));
             done();
           });
-          element._cache[cacheKey] = 'fake cache';
+          element._cache.set(cacheKey, 'fake cache');
           stub.lastCall.args[0].errFn({status: 403});
         });
 
@@ -559,10 +564,10 @@
 
       element.getAccount().then(response => {
         assert.isTrue(element._fetchSharedCacheURL.called);
-        assert.equal(element._cache[cacheKey], 'fake cache');
+        assert.equal(element._cache.get(cacheKey), 'fake cache');
         done();
       });
-      element._cache[cacheKey] = 'fake cache';
+      element._cache.set(cacheKey, 'fake cache');
 
       stub.lastCall.args[0].errFn({});
     });
@@ -728,7 +733,7 @@
 
     test('setAccountStatus', () => {
       sandbox.stub(element, '_send').returns(Promise.resolve('OOO'));
-      element._cache['/accounts/self/detail'] = {};
+      element._cache.set('/accounts/self/detail', {});
       return element.setAccountStatus('OOO').then(() => {
         assert.isTrue(element._send.calledOnce);
         assert.equal(element._send.lastCall.args[0].method, 'PUT');
@@ -736,7 +741,7 @@
             '/accounts/self/status');
         assert.deepEqual(element._send.lastCall.args[0].body,
             {status: 'OOO'});
-        assert.deepEqual(element._cache['/accounts/self/detail'],
+        assert.deepEqual(element._cache.get('/accounts/self/detail'),
             {status: 'OOO'});
       });
     });
@@ -830,7 +835,7 @@
           Promise.resolve([change_num, file_name, file_contents]));
       sandbox.stub(element, 'getResponseObject')
           .returns(Promise.resolve([change_num, file_name, file_contents]));
-      element._cache['/changes/' + change_num + '/edit/' + file_name] = {};
+      element._cache.set('/changes/' + change_num + '/edit/' + file_name, {});
       return element.saveChangeEdit(change_num, file_name, file_contents)
           .then(() => {
             assert.isTrue(element._send.calledOnce);
@@ -849,7 +854,7 @@
           Promise.resolve([change_num, message]));
       sandbox.stub(element, 'getResponseObject')
           .returns(Promise.resolve([change_num, message]));
-      element._cache['/changes/' + change_num + '/message'] = {};
+      element._cache.set('/changes/' + change_num + '/message', {});
       return element.putChangeCommitMessage(change_num, message).then(() => {
         assert.isTrue(element._send.calledOnce);
         assert.equal(element._send.lastCall.args[0].method, 'PUT');
@@ -1031,7 +1036,8 @@
         const changeNum = 4321;
         element._projectLookup[changeNum] = 'test';
         const params = {foo: 'bar'};
-        const expectedUrl = '/changes/test~4321/detail?foo=bar';
+        const expectedUrl =
+            window.CANONICAL_PATH + '/changes/test~4321/detail?foo=bar';
         sandbox.stub(element._etags, 'getOptions');
         sandbox.stub(element._etags, 'collect');
         return element._getChangeDetail(changeNum, params).then(() => {