diff --git a/packages/recs/src/Component.ts b/packages/recs/src/Component.ts
index d65796c091..bd4ba16b8e 100644
--- a/packages/recs/src/Component.ts
+++ b/packages/recs/src/Component.ts
@@ -145,7 +145,7 @@ export function overridableComponent<S extends Schema>(component: Component<S>):
   const overrides = new Map<string, { update: Override<S>; nonce: number }>();
 
   // Map from EntityIndex to current overridden component value
-  const overriddenEntityValues = new Map<EntityIndex, Partial<ComponentValue<S>>>();
+  const overriddenEntityValues = new Map<EntityIndex, Partial<ComponentValue<S>> | null>();
 
   // Update event stream that takes into account overridden entity values
   const update$ = new Subject<{
@@ -188,7 +188,7 @@ export function overridableComponent<S extends Schema>(component: Component<S>):
   function getOverriddenComponentValue(entity: EntityIndex): ComponentValue<S> | undefined {
     const originalValue = getComponentValue(component, entity);
     const overriddenValue = overriddenEntityValues.get(entity);
-    return originalValue || overriddenValue
+    return (originalValue || overriddenValue) && overriddenValue !== null // null is a valid override, in this case return undefined
       ? ({ ...originalValue, ...overriddenValue } as ComponentValue<S>)
       : undefined;
   }
@@ -241,9 +241,10 @@ export function overridableComponent<S extends Schema>(component: Component<S>):
   }) as OverridableComponent<S>;
 
   // Internal function to set the current overridden component value and emit the update event
-  function setOverriddenComponentValue(entity: EntityIndex, value?: Partial<ComponentValue<S>>) {
+  function setOverriddenComponentValue(entity: EntityIndex, value?: Partial<ComponentValue<S>> | null) {
+    // Check specifically for undefined - null is a valid override
     const prevValue = getOverriddenComponentValue(entity);
-    if (value) overriddenEntityValues.set(entity, value);
+    if (value !== undefined) overriddenEntityValues.set(entity, value);
     else overriddenEntityValues.delete(entity);
     update$.next({ entity, value: [getOverriddenComponentValue(entity), prevValue], component: overriddenComponent });
   }
diff --git a/packages/recs/src/World.ts b/packages/recs/src/World.ts
index dda390f10a..83149ea138 100644
--- a/packages/recs/src/World.ts
+++ b/packages/recs/src/World.ts
@@ -15,7 +15,13 @@ export function createWorld() {
 
   function registerEntity({ id, idSuffix }: { id?: EntityID; idSuffix?: string } = {}) {
     const entity = (id || entities.length + (idSuffix ? "-" + idSuffix : "")) as EntityID;
-    const index = (entities.push(entity) - 1) as EntityIndex;
+
+    // Skip if entity already exists
+    let index = entityToIndex.get(entity);
+    if (index != null) return index;
+
+    // Register entity
+    index = (entities.push(entity) - 1) as EntityIndex;
     entityToIndex.set(entity, index);
     return index;
   }
diff --git a/packages/recs/src/types.ts b/packages/recs/src/types.ts
index b33087800e..be102c7060 100644
--- a/packages/recs/src/types.ts
+++ b/packages/recs/src/types.ts
@@ -150,7 +150,7 @@ export type SchemaOf<C extends Component<Schema>> = C extends Component<infer S>
 
 export type Override<T extends Schema> = {
   entity: EntityIndex;
-  value: Partial<ComponentValue<T>>;
+  value: Partial<ComponentValue<T>> | null;
 };
 
 export type OverridableComponent<T extends Schema = Schema> = Component<T> & {
diff --git a/packages/recs/tests/System.spec.ts b/packages/recs/tests/System.spec.ts
index b7f80f5f30..9586098914 100644
--- a/packages/recs/tests/System.spec.ts
+++ b/packages/recs/tests/System.spec.ts
@@ -22,7 +22,7 @@ describe("System", () => {
       entity = createEntity(world, [withValue(Position, { x: 1, y: 2 })]);
     });
 
-    it("defineSystem should rerun the system if the query result changes (enter, update, exit)", () => {
+    it.only("defineSystem should rerun the system if the query result changes (enter, update, exit)", () => {
       const mock = jest.fn();
       defineSystem(world, [Has(Position)], mock);