diff --git a/build-system/tasks/presubmit-checks.js b/build-system/tasks/presubmit-checks.js
index 29d384e149b9..07c3eb3593f1 100644
--- a/build-system/tasks/presubmit-checks.js
+++ b/build-system/tasks/presubmit-checks.js
@@ -69,6 +69,14 @@ var forbiddenTerms = {
       'test/functional/test-cid.js',
     ],
   },
+  'getBaseCid': {
+    message: requiresReviewPrivacy,
+    whitelist: [
+      'src/service/cid-impl.js',
+      'src/viewer.js',
+      'test/functional/test-cid.js',
+    ],
+  },
   'cookie\\W': {
     message: requiresReviewPrivacy,
     whitelist: [
diff --git a/src/service/cid-impl.js b/src/service/cid-impl.js
index 028724d10b7d..d0775e77a047 100644
--- a/src/service/cid-impl.js
+++ b/src/service/cid-impl.js
@@ -27,6 +27,7 @@ import {getCookie} from '../cookies';
 import {getService} from '../service';
 import {parseUrl} from '../url';
 import {timer} from '../timer';
+import {viewerFor} from '../viewer';
 import {sha384Base64} from
     '../../third_party/closure-library/sha384-generated';
 
@@ -182,6 +183,13 @@ function getBaseCid(cid, persistenceConsent) {
     cid.baseCid_ = stored.cid;
     return Promise.resolve(stored.cid);
   }
+  // If we are being embedded, try to get the base cid from the viewer.
+  // Note, that we never try to persist to localStorage in this case.
+  const viewer = viewerFor(win);
+  if (viewer.isEmbedded()) {
+    return viewer.getBaseCid();
+  }
+
   // We need to make a new one.
   const seed = getEntropy(win);
   const newVal = cid.sha384Base64_(seed);
@@ -208,7 +216,15 @@ function store(win, cidString) {
   const item = {};
   item['time'] = timer.now();
   item['cid'] = cidString;
-  win.localStorage.setItem('amp-cid', JSON.stringify(item));
+  const data = JSON.stringify(item);
+  try {
+    win.localStorage.setItem('amp-cid', data);
+  } catch (ignore) {
+    // Setting localStorage may fail. In practice we don't expect that to
+    // happen a lot (since we don't go anywhere near the quote, but
+    // in particular in Safari private browsing mode it always fails.
+    // In that case we just don't store anything, which is just fine.
+  }
 }
 
 /**
@@ -218,7 +234,12 @@ function store(win, cidString) {
  * @return {!BaseCidInfo|undefined}
  */
 function read(win) {
-  const val = win.localStorage.getItem('amp-cid');
+  let val;
+  try {
+    val = win.localStorage.getItem('amp-cid');
+  } catch (ignore) {
+    // If reading from localStorage fails, we assume it is empty.
+  }
   if (!val) {
     return undefined;
   }
diff --git a/src/viewer.js b/src/viewer.js
index e0f611c12fcb..7fbe55b66307 100644
--- a/src/viewer.js
+++ b/src/viewer.js
@@ -419,6 +419,14 @@ export class Viewer {
     return this.sendMessage_('popHistory', {stackIndex: stackIndex}, true);
   }
 
+  /**
+   * Retrieves the Base CID from the viewer
+   * @return {!Promise<string>}
+   */
+  getBaseCid() {
+    return this.sendMessage_('cid', undefined, true);
+  }
+
   /**
    * Requests AMP document to receive a message from Viewer.
    * @param {string} eventType
diff --git a/test/functional/test-cid.js b/test/functional/test-cid.js
index 211d1395a439..f9c8fb12259a 100644
--- a/test/functional/test-cid.js
+++ b/test/functional/test-cid.js
@@ -19,10 +19,12 @@ import {installCidService, getSourceOrigin, isProxyOrigin} from
     '../../src/service/cid-impl';
 import {parseUrl} from '../../src/url';
 import {timer} from '../../src/timer';
+import {viewerFor} from '../../src/viewer';
 import * as sinon from 'sinon';
 
 describe('cid', () => {
 
+  let isEmbedded;
   let sandbox;
   let clock;
   let fakeWin;
@@ -32,6 +34,7 @@ describe('cid', () => {
 
   beforeEach(() => {
     let call = 1;
+    isEmbedded = false;
     sandbox = sinon.sandbox.create();
     clock = sandbox.useFakeTimers();
     storage = {};
@@ -63,6 +66,13 @@ describe('cid', () => {
         'amp-analytics': true
       }
     };
+    const viewer = viewerFor(fakeWin);
+    sandbox.stub(viewer, 'isEmbedded', function() {
+      return isEmbedded;
+    });
+    sandbox.stub(viewer, 'getBaseCid', function() {
+      return Promise.resolve('from-viewer');
+    });
     installCidService(fakeWin);
     return cidFor(fakeWin).then(c => {
       cid = c;
@@ -162,6 +172,25 @@ describe('cid', () => {
         'sha384(YYYhttp://www.origin.come2)');
   });
 
+  it('should retrieve cid from viewer if embedded', () => {
+    isEmbedded = true;
+    return compare(
+        'e2',
+        'sha384(from-viewerhttp://www.origin.come2)');
+  });
+
+  it('should prefer value in storage if present', () => {
+    isEmbedded = true;
+    storage['amp-cid'] = JSON.stringify({
+      cid: 'in-storage',
+      time: timer.now(),
+    });
+    return compare(
+        'e2',
+        'sha384(in-storagehttp://www.origin.come2)');
+  });
+
+
   it('should work without mocking', () => {
     const win = {
       location: {
@@ -174,6 +203,7 @@ describe('cid', () => {
     };
     win.__proto__ = window;
     expect(win.location.href).to.equal('https://cdn.ampproject.org/v/www.origin.com/');
+    viewerFor(win).isEmbedded = () => false;
     installCidService(win);
     return cidFor(win).then(cid => {
       return cid.get('foo', hasConsent).then(c1 => {