diff --git a/package.json b/package.json
index 0ab2c2a..feacdd1 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,7 @@
 	},
 	"scripts": {
 		"build": "del distribution && tsc",
-		"test": "tsc --noEmit && xo && ava && node test/test-node.js",
+		"test": "tsc --noEmit && xo && ava",
 		"prepare": "npm run build"
 	},
 	"files": [
diff --git a/source/index.ts b/source/index.ts
index aa68c81..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) && /^class(\s|{)/.test(value.toString());
+	return isFunction(value) && /^class(\s+|{)/.test(value.toString());
 }
 
 export function isDataView(value: unknown): value is DataView {
diff --git a/test/test-node.js b/test/test-node.js
deleted file mode 100644
index e742b87..0000000
--- a/test/test-node.js
+++ /dev/null
@@ -1,15 +0,0 @@
-import assert from 'node:assert';
-import {test} from 'node:test';
-import is, {assert as isAssert} from '../distribution/index.js';
-
-// Note: this test is separate from the rest of the tests, as it requires
-// preserving whitespace. The tsimp modifies the source and does not
-// properly preserve the intended test case
-test('is.class', () => {
-	const minifiedClass = class{}; // eslint-disable-line keyword-spacing
-	assert.ok(is.class(minifiedClass));
-
-	assert.doesNotThrow(() => {
-		isAssert.class(minifiedClass);
-	});
-});
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) {