diff --git a/__tests__/map-set.js b/__tests__/map-set.js
index 7ba25927..faa46803 100644
--- a/__tests__/map-set.js
+++ b/__tests__/map-set.js
@@ -235,5 +235,14 @@ function runBaseTest(name, useProxies, autoFreeze, useListener) {
 			})
 			expect(Array.from(set).sort()).toEqual([1, 2, 3])
 		})
+
+		test("#627 - new map key with value=undefined", () => {
+			const map = new Map()
+			const map1 = produce(map, draft => {
+				draft.set("key", undefined)
+			})
+			expect(map1.has("key")).toBe(true)
+			expect(map1.get("key")).toBe(undefined)
+		})
 	})
 }
diff --git a/src/plugins/mapset.ts b/src/plugins/mapset.ts
index 8e5b111c..8bb2d096 100644
--- a/src/plugins/mapset.ts
+++ b/src/plugins/mapset.ts
@@ -80,7 +80,7 @@ export function enableMapSet() {
 		p.set = function(key: any, value: any) {
 			const state: MapState = this[DRAFT_STATE]
 			assertUnrevoked(state)
-			if (latest(state).get(key) !== value) {
+			if (!latest(state).has(key) || latest(state).get(key) !== value) {
 				prepareMapCopy(state)
 				markChanged(state)
 				state.assigned_!.set(key, true)