diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
index eb23c616b2..ef036e6914 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.js
@@ -128,6 +128,8 @@
       'a': '_handleAKey',
       'd': '_handleDKey',
       'u': '_handleUKey',
+      'x': '_handleXKey',
+      'z': '_handleZKey',
     },
 
     attached: function() {
@@ -643,6 +645,22 @@
       this._determinePageBack();
     },
 
+    _handleXKey: function(e) {
+      if (this.shouldSuppressKeyboardShortcut(e) ||
+          this.modifierPressed(e)) { return; }
+
+      e.preventDefault();
+      this.$.messageList.handleExpandCollapse(true);
+    },
+
+    _handleZKey: function(e) {
+      if (this.shouldSuppressKeyboardShortcut(e) ||
+          this.modifierPressed(e)) { return; }
+
+      e.preventDefault();
+      this.$.messageList.handleExpandCollapse(false);
+    },
+
     _determinePageBack: function() {
       // Default backPage to '/' if user came to change view page
       // via an email link, etc.
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html
index c92d97a332..d5688f9671 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_test.html
@@ -79,6 +79,20 @@ limitations under the License.
         assert.isFalse(overlayEl.opened);
       });
 
+      test('X should expand all messages', function() {
+        var handleExpand =
+            sandbox.stub(element.$.messageList, 'handleExpandCollapse');
+        MockInteractions.pressAndReleaseKeyOn(element, 88, null, 'x');
+        assert(handleExpand.calledWith(true));
+      });
+
+      test('Z should collapse all messages', function() {
+         var handleExpand =
+            sandbox.stub(element.$.messageList, 'handleExpandCollapse');
+        MockInteractions.pressAndReleaseKeyOn(element, 90, null, 'z');
+        assert(handleExpand.calledWith(false));
+      });
+
       test('shift + R should fetch and navigate to the latest patch set',
           function(done) {
         element._changeNum = '42';
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.js b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.js
index dc98527c59..4dd9625d58 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.js
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list.js
@@ -106,15 +106,22 @@
       el.classList.add('highlighted');
     },
 
-    _handleExpandCollapseTap: function(e) {
-      e.preventDefault();
-      this._expanded = !this._expanded;
+    /**
+    * @param {boolean} expand
+    */
+    handleExpandCollapse: function(expand) {
+      this._expanded = expand;
       var messageEls = Polymer.dom(this.root).querySelectorAll('gr-message');
       for (var i = 0; i < messageEls.length; i++) {
-        messageEls[i].expanded = this._expanded;
+        messageEls[i].expanded = expand;
       }
     },
 
+    _handleExpandCollapseTap: function(e) {
+      e.preventDefault();
+      this.handleExpandCollapse(!this._expanded);
+    },
+
     _handleAutomatedMessageToggleTap: function(e) {
       e.preventDefault();
       this._hideAutomated = !this._hideAutomated;
diff --git a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html
index 51acebab1f..770da61ad2 100644
--- a/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html
+++ b/polygerrit-ui/app/elements/change/gr-messages-list/gr-messages-list_test.html
@@ -86,6 +86,29 @@ limitations under the License.
       }
     });
 
+    test('expand/collapse from external keypress', function() {
+      element.handleExpandCollapse(true);
+      var allMessageEls =
+          Polymer.dom(element.root).querySelectorAll('gr-message');
+      for (var i = 0; i < allMessageEls.length; i++) {
+        assert.isTrue(allMessageEls[i].expanded);
+      }
+
+      // Expand/collapse all text also changes.
+      assert.equal(element.$$('#collapse-messages').textContent.trim(),
+        'Collapse all');
+
+      element.handleExpandCollapse(false);
+      var allMessageEls =
+          Polymer.dom(element.root).querySelectorAll('gr-message');
+      for (var i = 0; i < allMessageEls.length; i++) {
+        assert.isFalse(allMessageEls[i].expanded);
+      }
+      // Expand/collapse all text also changes.
+      assert.equal(element.$$('#collapse-messages').textContent.trim(),
+        'Expand all');
+    });
+
     test('hide messages does not appear when no automated messages',
         function() {
       assert.isOk(element.$$('#automatedMessageToggleContainer[hidden]'));