diff --git a/src/service/viewer-impl.js b/src/service/viewer-impl.js
index 86060b19ae67..5d95786eee91 100644
--- a/src/service/viewer-impl.js
+++ b/src/service/viewer-impl.js
@@ -259,14 +259,14 @@ export class Viewer {
 
     /** @private {string} */
     this.unconfirmedReferrerUrl_ =
-        this.isEmbedded() && this.params_['referrer'] &&
+        this.isEmbedded() && 'referrer' in this.params_ &&
             trustedViewerResolved !== false ?
         this.params_['referrer'] :
         this.win.document.referrer;
 
     /** @const @private {!Promise<string>} */
     this.referrerUrl_ = new Promise(resolve => {
-      if (this.isEmbedded() && this.params_['referrer']) {
+      if (this.isEmbedded() && 'referrer' in this.params_) {
         // Viewer override, but only for whitelisted viewers. Only allowed for
         // iframed documents.
         this.isTrustedViewer_.then(isTrusted => {
diff --git a/test/functional/test-viewer.js b/test/functional/test-viewer.js
index 65d113c69edb..b157c419ec10 100644
--- a/test/functional/test-viewer.js
+++ b/test/functional/test-viewer.js
@@ -435,5 +435,19 @@ describe('Viewer', () => {
         expect(timeouts).to.have.length(0);
       });
     });
+
+    it('should allow override to empty if iframed and trusted', () => {
+      windowApi.parent = {};
+      windowApi.location.hash = '#referrer=';
+      windowApi.document.referrer = 'https://acme.org/docref';
+      windowApi.location.ancestorOrigins = ['https://google.com'];
+      const viewer = new Viewer(windowApi);
+      expect(viewer.getUnconfirmedReferrerUrl())
+          .to.equal('');
+      return viewer.getReferrerUrl().then(referrerUrl => {
+        expect(referrerUrl).to.equal('');
+        expect(timeouts).to.have.length(0);
+      });
+    });
   });
 });