diff --git a/__tests__/patch.js b/__tests__/patch.js
index f74dd5de..2a30f994 100644
--- a/__tests__/patch.js
+++ b/__tests__/patch.js
@@ -977,3 +977,22 @@ test.skip("#468", () => {
 	const final = applyPatches(state, patches)
 	expect(final).toEqual(nextState)
 })
+
+test("#521", () => {
+	const state = new Map()
+
+	const [nextState, patches] = produceWithPatches(state, draft => {
+		draft.set("hello", new Set(["world"]))
+	})
+
+	let patchedState = applyPatches(state, patches)
+	expect(patchedState).toEqual(nextState)
+
+	const [nextStateV2, patchesV2] = produceWithPatches(nextState, draft => {
+		draft.get("hello").add("immer")
+	})
+
+	expect(applyPatches(nextState, patchesV2)).toEqual(
+		new Map([["hello", new Set(["world", "immer"])]])
+	)
+})
diff --git a/src/patches.ts b/src/patches.ts
index 74135fd5..e2ba2752 100644
--- a/src/patches.ts
+++ b/src/patches.ts
@@ -14,7 +14,8 @@ import {
 	ES5ObjectState,
 	ProxyObjectState,
 	Archtype,
-	isMap
+	isMap,
+	isSet
 } from "./internal"
 
 export type PatchPath = (string | number)[]
@@ -255,7 +256,7 @@ function deepClonePatchValue(obj: any) {
 		return new Map(
 			Array.from(obj.entries()).map(([k, v]) => [k, deepClonePatchValue(v)])
 		)
-	// Not needed: if (isSet(obj)) return new Set(Array.from(obj.values()).map(deepClone))
+	if (isSet(obj)) return new Set(Array.from(obj).map(deepClonePatchValue))
 	const cloned = Object.create(Object.getPrototypeOf(obj))
 	for (const key in obj) cloned[key] = deepClonePatchValue(obj[key])
 	return cloned