diff --git a/src/mol-base/collections/integer/impl/sorted-array.ts b/src/mol-base/collections/integer/impl/sorted-array.ts
index 30c7292fc74a251961f607dc9f24019c4b992c42..1a6351b2532745a36bd5a740ebc5b309550a2339 100644
--- a/src/mol-base/collections/integer/impl/sorted-array.ts
+++ b/src/mol-base/collections/integer/impl/sorted-array.ts
@@ -15,7 +15,7 @@ export function ofSortedArray(xs: Nums) {
     return xs;
 }
 export function ofUnsortedArray(xs: Nums) { sortArray(xs); return xs; }
-export function is(xs: any): xs is Nums { return xs && (xs instanceof Array || !!xs.buffer); }
+export function is(xs: any): xs is Nums { return xs && (Array.isArray(xs) || !!xs.buffer); }
 
 export function start(xs: Nums) { return xs[0]; }
 export function end(xs: Nums) { return xs[xs.length - 1] + 1;  }
diff --git a/src/mol-data/atom-set/base.ts b/src/mol-data/atom-set/base.ts
index e457f8dc93a69730b9237ce935af4d993ee7ef69..3fba4183b0e09d9ee25214baa1dacedf3eee7b58 100644
--- a/src/mol-data/atom-set/base.ts
+++ b/src/mol-data/atom-set/base.ts
@@ -176,7 +176,7 @@ export function values(set: AtomSetImpl): Iterator<Atom> {
 }
 
 function isArrayLike(x: any): x is ArrayLike<Atom> {
-    return x && (typeof x.length === 'number' && (x instanceof Array || !!x.buffer));
+    return x && (typeof x.length === 'number' && (Array.isArray(x) || !!x.buffer));
 }
 
 function ofObject(data: { [id: number]: OrderedSet }) {