diff --git a/src/e2ee/CryptoClient.ts b/src/e2ee/CryptoClient.ts
index 0adcc4b0..b5d69860 100644
--- a/src/e2ee/CryptoClient.ts
+++ b/src/e2ee/CryptoClient.ts
@@ -123,6 +123,10 @@ export class CryptoClient {
      */
     public async onRoomJoin(roomId: string) {
         await this.roomTracker.onRoomJoin(roomId);
+        if (await this.isRoomEncrypted(roomId)) {
+            const members = await this.client.getRoomMembers(roomId, null, ['join', 'invite']);
+            await this.engine.addTrackedUsers(members.map(e => e.membershipFor));
+        }
     }
 
     /**
diff --git a/test/encryption/CryptoClientTest.ts b/test/encryption/CryptoClientTest.ts
index 02ed769e..5f9a3d2d 100644
--- a/test/encryption/CryptoClientTest.ts
+++ b/test/encryption/CryptoClientTest.ts
@@ -555,5 +555,45 @@ describe('CryptoClient', () => {
             // end up not running fast enough for our callCount checks.
             await Promise.all([prom1, prom2]);
         });
+
+        it('should update the tracked users when joining a new room', async () => {
+            // Stub the room tracker
+            (client.crypto as any).roomTracker.onRoomJoin = () => {};
+
+            const targetUserIds = ["@bob:example.org", "@charlie:example.org"];
+            const prom1 = new Promise<void>(extResolve => {
+                (client.crypto as any).engine.addTrackedUsers = simple.mock().callFn((uids) => {
+                    expect(uids).toEqual(targetUserIds);
+                    extResolve();
+                    return Promise.resolve();
+                });
+            });
+
+            const roomId = "!room:example.org";
+            const prom2 = new Promise<void>(extResolve => {
+                client.getRoomMembers = simple.mock().callFn((rid, token, memberships) => {
+                    expect(rid).toEqual(roomId);
+                    expect(token).toBeFalsy();
+                    expect(memberships).toEqual(["join", "invite"]);
+                    extResolve();
+                    return Promise.resolve(targetUserIds.map(u => new MembershipEvent({
+                        type: "m.room.member",
+                        state_key: u,
+                        content: { membership: "join" },
+                        sender: u,
+                    })));
+                });
+            });
+
+            client.crypto.isRoomEncrypted = async (rid) => {
+                expect(rid).toEqual(roomId);
+                return true;
+            };
+            client.emit("room.join", roomId);
+
+            // We do weird promise things because `emit()` is sync and we're using async code, so it can
+            // end up not running fast enough for our callCount checks.
+            await Promise.all([prom1, prom2]);
+        });
     });
 });