diff --git a/src/crypto/verification/SAS.ts b/src/crypto/verification/SAS.ts
index a7119d899..806b4bf5e 100644
--- a/src/crypto/verification/SAS.ts
+++ b/src/crypto/verification/SAS.ts
@@ -217,7 +217,7 @@ const MAC_SET = new Set(MAC_LIST);
 const SAS_SET = new Set(SAS_LIST);
 
 function intersection<T>(anArray: T[], aSet: Set<T>): T[] {
-    return anArray instanceof Array ? anArray.filter(x => aSet.has(x)) : [];
+    return Array.isArray(anArray) ? anArray.filter(x => aSet.has(x)) : [];
 }
 
 export enum SasEvent {
diff --git a/src/sliding-sync-sdk.ts b/src/sliding-sync-sdk.ts
index 5b02ca0c5..ed7ef9cb5 100644
--- a/src/sliding-sync-sdk.ts
+++ b/src/sliding-sync-sdk.ts
@@ -82,7 +82,7 @@ class ExtensionE2EE implements Extension {
             const unusedFallbackKeys = data["device_unused_fallback_key_types"] ||
                 data["org.matrix.msc2732.device_unused_fallback_key_types"];
             this.crypto.setNeedsNewFallback(
-                unusedFallbackKeys instanceof Array &&
+                Array.isArray(unusedFallbackKeys) &&
                 !unusedFallbackKeys.includes("signed_curve25519"),
             );
         }
diff --git a/src/sync.ts b/src/sync.ts
index 658b502db..5f5e2e13a 100644
--- a/src/sync.ts
+++ b/src/sync.ts
@@ -1482,7 +1482,7 @@ export class SyncApi {
             const unusedFallbackKeys = data["device_unused_fallback_key_types"] ||
                 data["org.matrix.msc2732.device_unused_fallback_key_types"];
             this.opts.crypto.setNeedsNewFallback(
-                unusedFallbackKeys instanceof Array &&
+                Array.isArray(unusedFallbackKeys) &&
                 !unusedFallbackKeys.includes("signed_curve25519"),
             );
         }
diff --git a/src/utils.ts b/src/utils.ts
index 237d1279e..c70ac914d 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -232,7 +232,7 @@ export function deepCompare(x: any, y: any): boolean {
     }
 
     // the object algorithm works for Array, but it's sub-optimal.
-    if (x instanceof Array) {
+    if (Array.isArray(x)) {
         if (x.length !== y.length) {
             return false;
         }