diff --git a/src/Umbraco.Web.UI.Client/src/libs/observable-api/array-state.ts b/src/Umbraco.Web.UI.Client/src/libs/observable-api/array-state.ts
index 954b4d3778..afdb6635b5 100644
--- a/src/Umbraco.Web.UI.Client/src/libs/observable-api/array-state.ts
+++ b/src/Umbraco.Web.UI.Client/src/libs/observable-api/array-state.ts
@@ -12,7 +12,7 @@ import { pushToUniqueArray } from './push-to-unique-array.function.js';
  * The ArrayState provides methods to append data when the data is an Object.
  */
 export class UmbArrayState<T> extends UmbDeepState<T[]> {
-	getUnique: (entry: T) => unknown;
+	readonly getUnique: (entry: T) => unknown;
 	#sortMethod?: (a: T, b: T) => number;
 
 	constructor(initialData: T[], getUniqueMethod: (entry: T) => unknown) {