diff --git a/packages/happy-dom/src/nodes/parent-node/ParentNodeUtility.ts b/packages/happy-dom/src/nodes/parent-node/ParentNodeUtility.ts
index 75dc2e51..6f5b218f 100644
--- a/packages/happy-dom/src/nodes/parent-node/ParentNodeUtility.ts
+++ b/packages/happy-dom/src/nodes/parent-node/ParentNodeUtility.ts
@@ -83,9 +83,14 @@ export default class ParentNodeUtility {
 		parentNode: Element | DocumentFragment | Document,
 		className: string
 	): HTMLCollection<Element> {
+		const classNames = className
+			// classNames can be whitespace separated, as many spaces as you want
+			.split(/\s+/)
+			.map((className) => `.${className}`)
+			.join('');
 		return new HTMLCollection(
 			PropertySymbol.illegalConstructor,
-			() => QuerySelector.querySelectorAll(parentNode, `.${className}`)[PropertySymbol.items]
+			() => QuerySelector.querySelectorAll(parentNode, classNames)[PropertySymbol.items]
 		);
 	}
 
diff --git a/packages/happy-dom/test/nodes/parent-node/ParentNodeUtility.test.ts b/packages/happy-dom/test/nodes/parent-node/ParentNodeUtility.test.ts
index 45bb92fe..b5f813a4 100644
--- a/packages/happy-dom/test/nodes/parent-node/ParentNodeUtility.test.ts
+++ b/packages/happy-dom/test/nodes/parent-node/ParentNodeUtility.test.ts
@@ -153,6 +153,32 @@ describe('ParentNodeUtility', () => {
 			expect(elementByClassName[1]).toBe(element2);
 			expect(elementByClassName[2]).toBe(element3);
 		});
+
+		it('Supports space-separated class names.', () => {
+			const addedClassName = 'className otherClassName verySeparatedClassName';
+			const queriedClassName = 'className otherClassName       verySeparatedClassName';
+
+			const parent = document.createElement('div');
+			const element1 = document.createElement('div');
+			const element2 = document.createElement('div');
+			const element3 = document.createElement('div');
+
+			element1.className = addedClassName;
+			element2.className = addedClassName;
+			element3.className = addedClassName;
+
+			parent.appendChild(element1);
+			element1.appendChild(element2);
+			element1.appendChild(element3);
+
+			const elementByClassName = ParentNodeUtility.getElementsByClassName(parent, queriedClassName);
+
+			expect(elementByClassName instanceof HTMLCollection).toBe(true);
+			expect(elementByClassName.length).toBe(3);
+			expect(elementByClassName[0]).toBe(element1);
+			expect(elementByClassName[1]).toBe(element2);
+			expect(elementByClassName[2]).toBe(element3);
+		});
 	});
 
 	describe('getElementsByTagName()', () => {