diff --git a/source/index.ts b/source/index.ts
index f40fad0..f5c8fdd 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -418,7 +418,7 @@ export function isBuffer(value: unknown): value is NodeBuffer {
 }
 
 export function isClass<T = unknown>(value: unknown): value is Class<T> {
-	return isFunction(value) && value.toString().startsWith('class ');
+	return isFunction(value) && /^class(\s+|{)/.test(value.toString());
 }
 
 export function isDataView(value: unknown): value is DataView {
diff --git a/test/test.ts b/test/test.ts
index 523bf11..4da5723 100644
--- a/test/test.ts
+++ b/test/test.ts
@@ -1086,9 +1086,13 @@ test('is.asyncIterable', t => {
 test('is.class', t => {
 	class Foo {} // eslint-disable-line @typescript-eslint/no-extraneous-class
 
+	// Note: Using new Function to prevent whitespace modifications in tsimp
+	const minifiedClass = new Function('return class{};'); // eslint-disable-line no-new-func
+
 	const classDeclarations = [
 		Foo,
 		class Bar extends Foo {},
+		minifiedClass(),
 	];
 
 	for (const classDeclaration of classDeclarations) {