diff --git a/packages/happy-dom/src/selection/Selection.ts b/packages/happy-dom/src/selection/Selection.ts
index b142cbdd6..3504d0bfe 100644
--- a/packages/happy-dom/src/selection/Selection.ts
+++ b/packages/happy-dom/src/selection/Selection.ts
@@ -92,7 +92,7 @@ export default class Selection {
 	 */
 	public get anchorOffset(): number {
 		if (!this.#range) {
-			return null;
+			return 0;
 		}
 		return this.#direction === SelectionDirectionEnum.forwards
 			? this.#range.startOffset
diff --git a/packages/happy-dom/test/selection/Selection.test.ts b/packages/happy-dom/test/selection/Selection.test.ts
index cd722bbf1..5cec5d2fb 100644
--- a/packages/happy-dom/test/selection/Selection.test.ts
+++ b/packages/happy-dom/test/selection/Selection.test.ts
@@ -117,8 +117,8 @@ describe('Selection', () => {
 
 	for (const property of ['anchorOffset', 'baseOffset', 'focusOffset', 'extentOffset']) {
 		describe(`get ${property}()`, () => {
-			it('Returns null if no Range has been added.', () => {
-				expect(selection[property]).toBe(null);
+			it('Returns 0 if no Range has been added.', () => {
+				expect(selection[property]).toBe(0);
 			});
 
 			it(`Returns start offset of Range if direction is "${SelectionDirectionEnum.forwards}".`, () => {