diff --git a/src/types/ArraySchema.ts b/src/types/ArraySchema.ts
index 4b486166..b8dc99d7 100644
--- a/src/types/ArraySchema.ts
+++ b/src/types/ArraySchema.ts
@@ -162,6 +162,11 @@ export class ArraySchema<V = any> implements Array<V>, SchemaDecoderCallbacks {
     }
 
     setAt(index: number, value: V) {
+        if (value === undefined || value === null) {
+            console.error("ArraySchema items cannot be null nor undefined; Use `deleteAt(index)` instead.");
+            return;
+        }
+
         if (value['$changes'] !== undefined) {
             (value['$changes'] as ChangeTree).setParent(this, this.$changes.root, index);
         }
diff --git a/test/ArraySchemaTest.ts b/test/ArraySchemaTest.ts
index 0ba038d2..4abecc0a 100644
--- a/test/ArraySchemaTest.ts
+++ b/test/ArraySchemaTest.ts
@@ -5,7 +5,7 @@ import { State, Player } from "./Schema";
 import { ArraySchema, Schema, type, Reflection, filter, MapSchema, dumpChanges, filterChildren } from "../src";
 
 describe("ArraySchema Tests", () => {
-    xit("should allow to setAt an undefined value", () => {
+    it("should not crash when pushing an undefined value", () => {
         class Block extends Schema {
             @type("number") num: number;
         }
@@ -18,7 +18,7 @@ describe("ArraySchema Tests", () => {
 
         const decodedState = new State();
         decodedState.decode(state.encode());
-        assert.strictEqual(decodedState.blocks.length, 2);
+        assert.strictEqual(decodedState.blocks.length, 1);
         assert.ok(decodedState.blocks.at(0) instanceof Block);
         assert.ok(decodedState.blocks.at(1) === undefined);
     });