diff --git a/packages/collection/__tests__/collection.test-d.ts b/packages/collection/__tests__/collection.test-d.ts
new file mode 100644
index 000000000..3a9bedbb2
--- /dev/null
+++ b/packages/collection/__tests__/collection.test-d.ts
@@ -0,0 +1,16 @@
+import { expectTypeOf, test } from 'vitest';
+import { Collection, type ReadonlyCollection } from '../src/index.js';
+
+test('ReadonlyCollection#tap preserves the readonly type', () => {
+	const readonly: ReadonlyCollection<string, number> = new Collection([['a', 1]]);
+
+	expectTypeOf(readonly.tap(() => {})).toEqualTypeOf<ReadonlyCollection<string, number>>();
+	expectTypeOf(readonly.tap(() => {}, null)).toEqualTypeOf<ReadonlyCollection<string, number>>();
+});
+
+test('ReadonlyCollection#each preserves the readonly type', () => {
+	const readonly: ReadonlyCollection<string, number> = new Collection([['a', 1]]);
+
+	expectTypeOf(readonly.each(() => {})).toEqualTypeOf<ReadonlyCollection<string, number>>();
+	expectTypeOf(readonly.each(() => {}, null)).toEqualTypeOf<ReadonlyCollection<string, number>>();
+});
diff --git a/packages/collection/src/collection.ts b/packages/collection/src/collection.ts
index 9e2930ef4..f6800a181 100644
--- a/packages/collection/src/collection.ts
+++ b/packages/collection/src/collection.ts
@@ -5,9 +5,22 @@
  */
 export type ReadonlyCollection<Key, Value> = Omit<
 	Collection<Key, Value>,
-	keyof Map<Key, Value> | 'ensure' | 'reverse' | 'sort' | 'sweep'
+	keyof Map<Key, Value> | 'each' | 'ensure' | 'reverse' | 'sort' | 'sweep' | 'tap'
 > &
-	ReadonlyMap<Key, Value>;
+	ReadonlyMap<Key, Value> & {
+		each(
+			fn: (value: Value, key: Key, collection: ReadonlyCollection<Key, Value>) => void,
+		): ReadonlyCollection<Key, Value>;
+		each<This>(
+			fn: (this: This, value: Value, key: Key, collection: ReadonlyCollection<Key, Value>) => void,
+			thisArg: This,
+		): ReadonlyCollection<Key, Value>;
+		tap(fn: (collection: ReadonlyCollection<Key, Value>) => void): ReadonlyCollection<Key, Value>;
+		tap<This>(
+			fn: (this: This, collection: ReadonlyCollection<Key, Value>) => void,
+			thisArg: This,
+		): ReadonlyCollection<Key, Value>;
+	};
 
 export interface Collection<Key, Value> {
 	/**