diff --git a/src/observable/list/SortedArray.ts b/src/observable/list/SortedArray.ts
index abbfa481..c85cca27 100644
--- a/src/observable/list/SortedArray.ts
+++ b/src/observable/list/SortedArray.ts
@@ -18,8 +18,6 @@ import {BaseObservableList} from "./BaseObservableList";
 import {sortedIndex} from "../../utils/sortedIndex";
 import {findAndUpdateInArray} from "./common";
 
-declare function sortedIndex<T>(array: T[], value: T, comparator: (left: T, right: T) => number): number;
-
 export class SortedArray<T> extends BaseObservableList<T> {
     private _comparator: (left: T, right: T) => number;
     private _items: T[] = [];