diff --git a/roomserver/internal/api.go b/roomserver/internal/api.go
index 712c365a4..4efb0558f 100644
--- a/roomserver/internal/api.go
+++ b/roomserver/internal/api.go
@@ -123,6 +123,7 @@ func (r *RoomserverInternalAPI) SetFederationAPI(fsAPI fsAPI.RoomserverFederatio
 		ServerName:          r.ServerName,
 		SigningIdentity:     r.SigningIdentityFor,
 		FSAPI:               fsAPI,
+		RSAPI:               r,
 		KeyRing:             keyRing,
 		ACLs:                r.ServerACLs,
 		Queryer:             r.Queryer,
diff --git a/roomserver/internal/input/input.go b/roomserver/internal/input/input.go
index a8afbc313..990563599 100644
--- a/roomserver/internal/input/input.go
+++ b/roomserver/internal/input/input.go
@@ -83,6 +83,7 @@ type Inputer struct {
 	ServerName          spec.ServerName
 	SigningIdentity     func(ctx context.Context, roomID spec.RoomID, senderID spec.UserID) (fclient.SigningIdentity, error)
 	FSAPI               fedapi.RoomserverFederationAPI
+	RSAPI               api.RoomserverInternalAPI
 	KeyRing             gomatrixserverlib.JSONVerifier
 	ACLs                *acls.ServerACLs
 	InputRoomEventTopic string
diff --git a/roomserver/internal/input/input_events.go b/roomserver/internal/input/input_events.go
index 93f6cc015..4823a38af 100644
--- a/roomserver/internal/input/input_events.go
+++ b/roomserver/internal/input/input_events.go
@@ -448,6 +448,24 @@ func (r *Inputer) processRoomEvent(
 		return nil
 	}
 
+	// TODO: Revist this to ensure we don't replace a current state mxid_mapping with an older one.
+	if event.Type() == spec.MRoomMember {
+		mapping := gomatrixserverlib.MemberContent{}
+		if err := json.Unmarshal(event.Content(), &mapping); err != nil {
+			return err
+		}
+		if mapping.MXIDMapping != nil {
+			storeUserID, userErr := spec.NewUserID(mapping.MXIDMapping.UserID, true)
+			if userErr != nil {
+				return userErr
+			}
+			err = r.RSAPI.StoreUserRoomPublicKey(ctx, mapping.MXIDMapping.UserRoomKey, *storeUserID, *validRoomID)
+			if err != nil {
+				return fmt.Errorf("failed storing user room public key: %w", err)
+			}
+		}
+	}
+
 	switch input.Kind {
 	case api.KindNew:
 		if err = r.updateLatestEvents(
diff --git a/roomserver/internal/perform/perform_join.go b/roomserver/internal/perform/perform_join.go
index 937993ded..dfce9cc77 100644
--- a/roomserver/internal/perform/perform_join.go
+++ b/roomserver/internal/perform/perform_join.go
@@ -274,7 +274,6 @@ func (r *Joiner) performJoinRoomByID(
 	// If we should do a forced federated join then do that.
 	var joinedVia spec.ServerName
 	if forceFederatedJoin {
-		// TODO : pseudoIDs - pass through userID here since we don't know what the senderID should be yet
 		joinedVia, err = r.performFederatedJoinRoomByID(ctx, req)
 		return req.RoomIDOrAlias, joinedVia, err
 	}
@@ -286,10 +285,7 @@ func (r *Joiner) performJoinRoomByID(
 	// but everyone has since left. I suspect it does the wrong thing.
 
 	var buildRes rsAPI.QueryLatestEventsAndStateResponse
-	identity, err := r.RSAPI.SigningIdentityFor(ctx, *roomID, *userID)
-	if err != nil {
-		return "", "", fmt.Errorf("error joining local room: %q", err)
-	}
+	identity := r.Cfg.Matrix.SigningIdentity
 
 	// at this point we know we have an existing room
 	if inRoomRes.RoomVersion == gomatrixserverlib.RoomVersionPseudoIDs {