diff --git a/src/migrations.test.ts b/src/migrations.test.ts
index c466451..4108752 100644
--- a/src/migrations.test.ts
+++ b/src/migrations.test.ts
@@ -1,5 +1,5 @@
 import { PanelModel } from '@grafana/data';
-
+import { cloneDeep } from 'lodash';
 import { clockMigrationHandler } from './migrations';
 
 describe('Clock migrations', () => {
@@ -249,4 +249,33 @@ describe('Clock migrations', () => {
     expect(options).toMatchSnapshot();
     expect(panel).toMatchSnapshot();
   });
+
+  describe('support readonly targets in G12', () => {
+    it('should not try to mutate targets when migrating panel', () => {
+      const panel = createPanelWithReadonlyTargets({
+        options: {
+          countdownSettings: { source: 'input' },
+        },
+        datasource: { type: 'test', uid: '123' },
+        targets: [],
+      } as unknown as PanelModel);
+
+      expect(() => clockMigrationHandler(panel)).not.toThrow();
+    });
+  });
 });
+
+function createPanelWithReadonlyTargets(panel: Partial<PanelModel>): PanelModel {
+  // https://github.com/grafana/grafana/blob/2bbba880cd2a8269e262e4ea7138fcd43f4d5c66/public/app/features/dashboard-scene/serialization/angularMigration.ts#L18
+  const targetClone = cloneDeep(panel.targets);
+  Object.defineProperty(panel, 'targets', {
+    get: function () {
+      console.warn(
+        'Accessing the targets property when migrating a panel plugin is deprecated. Changes to this property will be ignored.'
+      );
+      return targetClone;
+    },
+  });
+
+  return panel as unknown as PanelModel;
+}
diff --git a/src/migrations.ts b/src/migrations.ts
index 16b010f..8277627 100644
--- a/src/migrations.ts
+++ b/src/migrations.ts
@@ -10,8 +10,10 @@ export const clockMigrationHandler = (panel: PanelModel<ClockOptions>): Partial<
     options.refresh = ClockRefresh.dashboard;
   }
 
-  if (detectInputOnlyPluginConfig(panel)) {
-    migrateInputOnlyPluginConfig(panel);
+  if (!isReadonlyTarget(panel)) {
+    if (detectInputOnlyPluginConfig(panel)) {
+      migrateInputOnlyPluginConfig(panel);
+    }
   }
   // configuration options moved as the panel migrated, clean up if needed
   cleanupConfig(panel);
@@ -159,3 +161,8 @@ const cleanupConfig = (panel: PanelModel<ClockOptions>) => {
     delete panel.timezoneSettings;
   }
 };
+
+function isReadonlyTarget(panel: PanelModel<ClockOptions, any>) {
+  const description = Object.getOwnPropertyDescriptor(panel, 'targets');
+  return typeof description?.set === 'undefined' && typeof description?.get === 'function';
+}