diff --git a/src/Membership/StandardRoomMembershipRevision.test.ts b/src/Membership/StandardRoomMembershipRevision.test.ts
new file mode 100644
index 0000000..c11504f
--- /dev/null
+++ b/src/Membership/StandardRoomMembershipRevision.test.ts
@@ -0,0 +1,26 @@
+// SPDX-FileCopyrightText: 2024 Gnuxie <Gnuxie@protonmail.com>
+//
+// SPDX-License-Identifier: AFL-3.0
+
+import { describeRoomMember } from '../StateTracking/DeclareRoomState';
+import { randomRoomID, randomUserID } from '../TestUtilities/EventGeneration';
+import { Membership } from './MembershipChange';
+import { StandardRoomMembershipRevision } from './StandardRoomMembershipRevision';
+
+test('Membership events are unintenrned', function () {
+  const joinLeaveUser = randomUserID();
+  const room = randomRoomID([]);
+  const joinEvent = describeRoomMember({
+    sender: joinLeaveUser,
+    room_id: room.toRoomIDOrAlias(),
+  });
+  const leaveEvent = describeRoomMember({
+    sender: joinLeaveUser,
+    room_id: room.toRoomIDOrAlias(),
+    membership: Membership.Leave,
+  });
+  const revision = StandardRoomMembershipRevision.blankRevision(room)
+    .reviseFromMembership([joinEvent])
+    .reviseFromMembership([leaveEvent]);
+  expect([...revision.members()].length).toBe(1);
+});
diff --git a/src/Membership/StandardRoomMembershipRevision.ts b/src/Membership/StandardRoomMembershipRevision.ts
index 3510e86..23172c2 100644
--- a/src/Membership/StandardRoomMembershipRevision.ts
+++ b/src/Membership/StandardRoomMembershipRevision.ts
@@ -126,6 +126,12 @@ export class StandardRoomMembershipRevision implements RoomMembershipRevision {
         change.userID,
         change
       );
+      const existingMembership = this.membershipForUser(change.userID);
+      if (existingMembership !== undefined) {
+        nextMembershipByEventID = nextMembershipByEventID.delete(
+          existingMembership.eventID
+        );
+      }
       nextMembershipByEventID = nextMembershipByEventID.set(
         change.eventID,
         change
diff --git a/src/TestUtilities/EventGeneration.ts b/src/TestUtilities/EventGeneration.ts
index 3e9a9d2..d05dffa 100644
--- a/src/TestUtilities/EventGeneration.ts
+++ b/src/TestUtilities/EventGeneration.ts
@@ -12,8 +12,10 @@ import {
   MatrixRoomReference,
 } from '../MatrixTypes/MatrixRoomReference';
 import {
+  StringEventID,
   StringRoomID,
   StringUserID,
+  isStringEventID,
   isStringRoomID,
   isStringUserID,
 } from '../MatrixTypes/StringlyTypedMatrix';
@@ -66,7 +68,7 @@ export function makePolicyRuleUserEvent({
   });
   const rawEventJSON = {
     room_id,
-    event_id: `$${randomUUID()}:example.com`,
+    event_id: randomEventID(),
     origin_server_ts: Date.now(),
     state_key: description.state_key,
     type: description.type,
@@ -109,3 +111,11 @@ export function randomUserID(): StringUserID {
   }
   return userID;
 }
+
+export function randomEventID(): StringEventID {
+  const eventID = `$${randomUUID()}:example.com`;
+  if (!isStringEventID(eventID)) {
+    throw new TypeError(`EventID generator is wrong`);
+  }
+  return eventID;
+}