diff --git a/src/crypto/index.ts b/src/crypto/index.ts
index 34f108a39..e718d2eb0 100644
--- a/src/crypto/index.ts
+++ b/src/crypto/index.ts
@@ -128,7 +128,7 @@ export interface IBootstrapCrossSigningOpts {
 }
 
 export interface ICryptoCallbacks {
-    getCrossSigningKey?: (keyType: string, pubKey: string) => Promise<Uint8Array>;
+    getCrossSigningKey?: (keyType: string, pubKey: string) => Promise<Uint8Array | null>;
     saveCrossSigningKeys?: (keys: Record<string, Uint8Array>) => void;
     shouldUpgradeDeviceVerifications?: (
         users: Record<string, any>
diff --git a/src/sliding-sync-sdk.ts b/src/sliding-sync-sdk.ts
index 06efc0a84..962d824a8 100644
--- a/src/sliding-sync-sdk.ts
+++ b/src/sliding-sync-sdk.ts
@@ -396,7 +396,7 @@ export class SlidingSyncSdk {
 
     public createRoom(roomId: string): Room { // XXX cargoculted from sync.ts
         const { timelineSupport } = this.client;
-        const room = new Room(roomId, this.client, this.client.getUserId(), {
+        const room = new Room(roomId, this.client, this.client.getUserId()!, {
             lazyLoadMembers: this.opts.lazyLoadMembers,
             pendingEventOrdering: this.opts.pendingEventOrdering,
             timelineSupport,
@@ -428,7 +428,7 @@ export class SlidingSyncSdk {
             RoomStateEvent.Update,
         ]);
         room.currentState.on(RoomStateEvent.NewMember, (event, state, member) => {
-            member.user = this.client.getUser(member.userId);
+            member.user = this.client.getUser(member.userId) ?? undefined;
             this.client.reEmitter.reEmit(member, [
                 RoomMemberEvent.Name,
                 RoomMemberEvent.Typing,