diff --git a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
index 8d91ef8..6a7966b 100644
--- a/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
+++ b/polygerrit-ui/app/elements/change/gr-reply-dialog/gr-reply-dialog_test.html
@@ -55,7 +55,7 @@
       stub('gr-rest-api-interface', {
         getConfig() { return Promise.resolve({}); },
         getAccount() { return Promise.resolve({}); },
-        getChange() { return Promise.resolve([{}]); },
+        getChange() { return Promise.resolve({}); },
         getChangeSuggestedReviewers() { return Promise.resolve([]); },
       });
 
diff --git a/polygerrit-ui/app/elements/core/gr-router/gr-router.js b/polygerrit-ui/app/elements/core/gr-router/gr-router.js
index dc264f2..d85b810 100644
--- a/polygerrit-ui/app/elements/core/gr-router/gr-router.js
+++ b/polygerrit-ui/app/elements/core/gr-router/gr-router.js
@@ -498,9 +498,12 @@
 
       return this.$.restAPI.getFromProjectLookup(params.changeNum)
           .then(project => {
-            // Do nothing if the lookup request failed. This avoids an infinite
-            // loop of project lookups.
-            if (!project) { return; }
+            // Show a 404 and terminate if the lookup request failed. Attempting
+            // to redirect after failing to get the project loops infinitely.
+            if (!project) {
+              this._show404();
+              return;
+            }
 
             params.project = project;
             this._normalizePatchRangeParams(params);
@@ -1333,6 +1336,10 @@
      * Catchall route for when no other route is matched.
      */
     _handleDefaultRoute() {
+      this._show404();
+    },
+
+    _show404() {
       // Note: the app's 404 display is tightly-coupled with catching 404
       // network responses, so we simulate a 404 response status to display it.
       // TODO: Decouple the gr-app error view from network responses.
diff --git a/polygerrit-ui/app/elements/core/gr-router/gr-router_test.html b/polygerrit-ui/app/elements/core/gr-router/gr-router_test.html
index 7011c65..4af8130 100644
--- a/polygerrit-ui/app/elements/core/gr-router/gr-router_test.html
+++ b/polygerrit-ui/app/elements/core/gr-router/gr-router_test.html
@@ -430,11 +430,13 @@
       suite('_normalizeLegacyRouteParams', () => {
         let rangeStub;
         let redirectStub;
+        let show404Stub;
 
         setup(() => {
           rangeStub = sandbox.stub(element, '_normalizePatchRangeParams')
               .returns(Promise.resolve());
           redirectStub = sandbox.stub(element, '_redirect');
+          show404Stub = sandbox.stub(element, '_show404');
         });
 
         test('w/o changeNum', () => {
@@ -445,6 +447,7 @@
             assert.isFalse(rangeStub.called);
             assert.isNotOk(params.project);
             assert.isFalse(redirectStub.called);
+            assert.isFalse(show404Stub.called);
           });
         });
 
@@ -456,18 +459,19 @@
             assert.isTrue(rangeStub.called);
             assert.equal(params.project, 'foo/bar');
             assert.isTrue(redirectStub.calledOnce);
+            assert.isFalse(show404Stub.called);
           });
         });
 
         test('halts on project lookup failure', () => {
           projectLookupStub.returns(Promise.resolve(undefined));
-
           const params = {changeNum: 1234};
           return element._normalizeLegacyRouteParams(params).then(() => {
             assert.isTrue(projectLookupStub.called);
             assert.isFalse(rangeStub.called);
             assert.isUndefined(params.project);
             assert.isFalse(redirectStub.called);
+            assert.isTrue(show404Stub.calledOnce);
           });
         });
       });
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 b5bb35a..3f19f7e 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
@@ -1993,7 +1993,11 @@
      */
     getChange(changeNum, opt_errFn) {
       // Cannot use _changeBaseURL, as this function is used by _projectLookup.
-      return this.fetchJSON(`/changes/?q=${changeNum}`, opt_errFn);
+      return this.fetchJSON(`/changes/?q=change:${changeNum}`, opt_errFn)
+          .then(res => {
+            if (!res || !res.length) { return null; }
+            return res[0];
+          });
     },
 
     /**
@@ -2026,8 +2030,7 @@
         this.fire('page-error', {response});
       };
 
-      return this.getChange(changeNum, onError).then(res => {
-        const change = res[0];
+      return this.getChange(changeNum, onError).then(change => {
         if (!change || !change.project) { return; }
         this.setInProjectLookup(changeNum, change.project);
         return change.project;
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 a8c09d1..33eb181 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
@@ -1036,7 +1036,7 @@
     suite('getFromProjectLookup', () => {
       test('getChange fails', () => {
         sandbox.stub(element, 'getChange')
-            .returns(Promise.resolve([]));
+            .returns(Promise.resolve(null));
         return element.getFromProjectLookup().then(val => {
           assert.strictEqual(val, undefined);
           assert.deepEqual(element._projectLookup, {});
@@ -1044,7 +1044,7 @@
       });
 
       test('getChange succeeds, no project', () => {
-        sandbox.stub(element, 'getChange').returns(Promise.resolve([]));
+        sandbox.stub(element, 'getChange').returns(Promise.resolve(null));
         return element.getFromProjectLookup().then(val => {
           assert.strictEqual(val, undefined);
           assert.deepEqual(element._projectLookup, {});
@@ -1053,7 +1053,7 @@
 
       test('getChange succeeds with project', () => {
         sandbox.stub(element, 'getChange')
-            .returns(Promise.resolve([{project: 'project'}]));
+            .returns(Promise.resolve({project: 'project'}));
         return element.getFromProjectLookup('test').then(val => {
           assert.equal(val, 'project');
           assert.deepEqual(element._projectLookup, {test: 'project'});