diff --git a/Documentation/js-api.txt b/Documentation/js-api.txt
index f3b84d2705..a28d062b41 100644
--- a/Documentation/js-api.txt
+++ b/Documentation/js-api.txt
@@ -167,7 +167,8 @@ Supported events:
 * `showchange`: Invoked when a change is made visible. A
   link:rest-api-changes.html#change-info[ChangeInfo] and
   link:rest-api-changes.html#revision-info[RevisionInfo]
-  are passed as arguments.
+  are passed as arguments. PolyGerrit provides a third parameter which
+  is an object with a `mergeable` boolean.
 
 * `submitchange`: Invoked when the submit button is clicked
   on a change. A link:rest-api-changes.html#change-info[ChangeInfo]
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 5718e8e1c4..5fdef79343 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
@@ -554,10 +554,7 @@
           patchRange.patchNum = this.computeLatestPatchNum(this._allPatchSets);
         }
         this._reloadPatchNumDependentResources().then(() => {
-          this.$.jsAPI.handleEvent(this.$.jsAPI.EventType.SHOW_CHANGE, {
-            change: this._change,
-            patchNum: patchRange.patchNum,
-          });
+          this._sendShowChangeEvent();
         });
         return;
       }
@@ -570,15 +567,20 @@
       });
     },
 
+    _sendShowChangeEvent() {
+      this.$.jsAPI.handleEvent(this.$.jsAPI.EventType.SHOW_CHANGE, {
+        change: this._change,
+        patchNum: this._patchRange.patchNum,
+        info: {mergeable: this._mergeable},
+      });
+    },
+
     _performPostLoadTasks() {
       this.$.relatedChanges.reload();
       this._maybeShowReplyDialog();
       this._maybeShowRevertDialog();
 
-      this.$.jsAPI.handleEvent(this.$.jsAPI.EventType.SHOW_CHANGE, {
-        change: this._change,
-        patchNum: this._patchRange.patchNum,
-      });
+      this._sendShowChangeEvent();
 
       this.async(() => {
         if (this.viewState.scrollTop) {
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 d02db0cc78..347100e0e4 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
@@ -1459,6 +1459,22 @@ limitations under the License.
       });
     });
 
+    test('_sendShowChangeEvent', () => {
+      element._change = {labels: {}};
+      element._patchRange = {patchNum: 4};
+      element._mergeable = true;
+      const showStub = sandbox.stub(element.$.jsAPI, 'handleEvent');
+      element._sendShowChangeEvent();
+      assert.isTrue(showStub.calledOnce);
+      assert.equal(
+          showStub.lastCall.args[0], element.$.jsAPI.EventType.SHOW_CHANGE);
+      assert.deepEqual(showStub.lastCall.args[1], {
+        change: {labels: {}},
+        patchNum: 4,
+        info: {mergeable: true},
+      });
+    });
+
     suite('_handleEditTap', () => {
       let fireEdit;
 
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.js b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.js
index 38262eccf4..d974b62469 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.js
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface.js
@@ -120,18 +120,34 @@
     },
 
     _handleShowChange(detail) {
-      for (const cb of this._getEventCallbacks(EventType.SHOW_CHANGE)) {
-        const change = detail.change;
-        const patchNum = detail.patchNum;
-        let revision;
-        for (const rev of Object.values(change.revisions || {})) {
-          if (this.patchNumEquals(rev._number, patchNum)) {
-            revision = rev;
-            break;
-          }
+      // Note (issue 8221) Shallow clone the change object and add a mergeable
+      // getter with deprecation warning. This makes the change detail appear as
+      // though SKIP_MERGEABLE was not set, so that plugins that expect it can
+      // still access.
+      //
+      // This clone and getter can be removed after plugins migrate to use
+      // info.mergeable.
+      const change = Object.assign({
+        get mergeable() {
+          console.warn('Accessing change.mergeable from SHOW_CHANGE is ' +
+              'deprecated! Use info.mergeable instead.');
+          return detail.info.mergeable;
+        },
+      }, detail.change);
+      const patchNum = detail.patchNum;
+      const info = detail.info;
+
+      let revision;
+      for (const rev of Object.values(change.revisions || {})) {
+        if (this.patchNumEquals(rev._number, patchNum)) {
+          revision = rev;
+          break;
         }
+      }
+
+      for (const cb of this._getEventCallbacks(EventType.SHOW_CHANGE)) {
         try {
-          cb(change, revision);
+          cb(change, revision, info);
         } catch (err) {
           console.error(err);
         }
diff --git a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
index 62c4a91eb9..5ad389533e 100644
--- a/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
+++ b/polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html
@@ -179,15 +179,17 @@ limitations under the License.
         _number: 42,
         revisions: {def: {_number: 2}, abc: {_number: 1}},
       };
+      const expectedChange = Object.assign({mergeable: false}, testChange);
       plugin.on(element.EventType.SHOW_CHANGE, throwErrFn);
-      plugin.on(element.EventType.SHOW_CHANGE, (change, revision) => {
-        assert.deepEqual(change, testChange);
+      plugin.on(element.EventType.SHOW_CHANGE, (change, revision, info) => {
+        assert.deepEqual(change, expectedChange);
         assert.deepEqual(revision, testChange.revisions.abc);
+        assert.deepEqual(info, {mergeable: false});
         assert.isTrue(errorStub.calledOnce);
         done();
       });
       element.handleEvent(element.EventType.SHOW_CHANGE,
-          {change: testChange, patchNum: 1});
+          {change: testChange, patchNum: 1, info: {mergeable: false}});
     });
 
     test('handleEvent awaits plugins load', done => {