diff --git a/source/is-union.d.ts b/source/is-union.d.ts
index 06ca80903..0e8e6a442 100644
--- a/source/is-union.d.ts
+++ b/source/is-union.d.ts
@@ -1,4 +1,5 @@
 import type {IsNever} from './is-never.d.ts';
+import type {IsEqual} from './is-equal.d.ts';
 
 /**
 Returns a boolean for whether the given type is a union.
@@ -24,7 +25,7 @@ type InternalIsUnion<T, U = T> =
 	IsNever<T> extends true
 		? false
 		: T extends any
-			? [U] extends [T]
+			? IsEqual<U, T> extends true
 				? false
 				: true
 			: never
diff --git a/test-d/is-union.ts b/test-d/is-union.ts
index 1258af3c8..2c1f5608b 100644
--- a/test-d/is-union.ts
+++ b/test-d/is-union.ts
@@ -16,3 +16,12 @@ expectType<IsUnion<'foo' | 'bar'>>(true);
 expectType<IsUnion<'foo' | 'bar' | 1>>(true);
 expectType<IsUnion<'foo' | 1>>(true);
 expectType<IsUnion<[] | {}>>(true);
+
+type TestUnion =
+	// Here, the entire union extends both the individual members:
+	// So, `TestUnion` extends `{opt?: number; a: number; b: string}`, and
+	// `TestUnion` extends `{a: number; b: string}`.
+	| {opt?: number; a: number; b: string}
+	| {a: number; b: string};
+
+expectType<IsUnion<TestUnion>>(true);