diff --git a/roomserver/api/api.go b/roomserver/api/api.go
index 99ec53719..ec1cd6abb 100644
--- a/roomserver/api/api.go
+++ b/roomserver/api/api.go
@@ -68,6 +68,7 @@ type InputRoomEventsAPI interface {
 type QuerySenderIDAPI interface {
 	// Accepts either roomID or alias
 	QuerySenderIDForUser(ctx context.Context, roomAliasOrID string, userID spec.UserID) (string, error)
+	QueryUserIDForSender(ctx context.Context, roomAliasOrID string, senderID string) (spec.UserID, error)
 }
 
 // Query the latest events and state for a room from the room server.
diff --git a/roomserver/internal/perform/perform_invite.go b/roomserver/internal/perform/perform_invite.go
index 7a12bc2cf..329395e63 100644
--- a/roomserver/internal/perform/perform_invite.go
+++ b/roomserver/internal/perform/perform_invite.go
@@ -97,11 +97,12 @@ func (r *Inviter) ProcessInviteMembership(
 ) ([]api.OutputEvent, error) {
 	var outputUpdates []api.OutputEvent
 	var updater *shared.MembershipUpdater
-	_, domain, err := gomatrixserverlib.SplitID('@', *inviteEvent.StateKey())
+
+	userID, err := r.RSAPI.QueryUserIDForSender(ctx, inviteEvent.RoomID(), *inviteEvent.StateKey())
 	if err != nil {
 		return nil, api.ErrInvalidID{Err: fmt.Errorf("the user ID %s is invalid", *inviteEvent.StateKey())}
 	}
-	isTargetLocal := r.Cfg.Matrix.IsLocalServerName(domain)
+	isTargetLocal := r.Cfg.Matrix.IsLocalServerName(userID.Domain())
 	if updater, err = r.DB.MembershipUpdater(ctx, inviteEvent.RoomID(), *inviteEvent.StateKey(), isTargetLocal, inviteEvent.Version()); err != nil {
 		return nil, fmt.Errorf("r.DB.MembershipUpdater: %w", err)
 	}
diff --git a/roomserver/internal/query/query.go b/roomserver/internal/query/query.go
index 15d226a74..d249b2896 100644
--- a/roomserver/internal/query/query.go
+++ b/roomserver/internal/query/query.go
@@ -1035,7 +1035,16 @@ func (r *Queryer) QueryRestrictedJoinAllowed(ctx context.Context, req *api.Query
 	return nil
 }
 
-func (r *Queryer) QuerySenderIDForRoom(ctx context.Context, roomAliasOrID string, userID spec.UserID) (string, error) {
+func (r *Queryer) QuerySenderIDForUser(ctx context.Context, roomAliasOrID string, userID spec.UserID) (string, error) {
 	// TODO: implement this properly with pseudoIDs
 	return userID.String(), nil
 }
+
+func (r *Queryer) QueryUserIDForSender(ctx context.Context, roomAliasOrID string, senderID string) (spec.UserID, error) {
+	// TODO: implement this properly with pseudoIDs
+	userID, err := spec.NewUserID(senderID, true)
+	if err != nil {
+		return spec.UserID{}, err
+	}
+	return *userID, err
+}