diff --git a/clientapi/routing/directory.go b/clientapi/routing/directory.go
index d9129d1bd..e914b2905 100644
--- a/clientapi/routing/directory.go
+++ b/clientapi/routing/directory.go
@@ -181,10 +181,37 @@ func SetLocalAlias(
 		return *resErr
 	}
 
+	maybeRoomID, err := spec.NewRoomID(r.RoomID)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: spec.InvalidParam("invalid room ID"),
+		}
+	}
+	roomID := *maybeRoomID // should be safe due to error check
+
+	maybeUserID, err := spec.NewUserID(device.UserID, true)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.Unknown("internal server error"),
+		}
+	}
+	userID := *maybeUserID
+
+	senderID, err := rsAPI.QuerySenderIDForUser(req.Context(), roomID, userID)
+	if err != nil {
+		util.GetLogger(req.Context()).WithError(err).Error("QuerySenderIDForUser failed")
+		return util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: spec.Unknown("internal server error"),
+		}
+	}
+
 	queryReq := roomserverAPI.SetRoomAliasRequest{
-		UserID: device.UserID,
-		RoomID: r.RoomID,
-		Alias:  alias,
+		SenderID: senderID,
+		RoomID:   r.RoomID,
+		Alias:    alias,
 	}
 	var queryRes roomserverAPI.SetRoomAliasResponse
 	if err := rsAPI.SetRoomAlias(req.Context(), &queryReq, &queryRes); err != nil {
diff --git a/roomserver/api/alias.go b/roomserver/api/alias.go
index c091cf6a3..5a6d48000 100644
--- a/roomserver/api/alias.go
+++ b/roomserver/api/alias.go
@@ -23,7 +23,7 @@ import (
 // SetRoomAliasRequest is a request to SetRoomAlias
 type SetRoomAliasRequest struct {
 	// ID of the user setting the alias
-	UserID string `json:"user_id"`
+	SenderID spec.SenderID `json:"sender"`
 	// New alias for the room
 	Alias string `json:"alias"`
 	// The room ID the alias is referring to
diff --git a/roomserver/internal/alias.go b/roomserver/internal/alias.go
index b04a56fe8..a3db9e97f 100644
--- a/roomserver/internal/alias.go
+++ b/roomserver/internal/alias.go
@@ -51,7 +51,7 @@ func (r *RoomserverInternalAPI) SetRoomAlias(
 	response.AliasExists = false
 
 	// Save the new alias
-	if err := r.DB.SetRoomAlias(ctx, request.Alias, request.RoomID, request.UserID); err != nil {
+	if err := r.DB.SetRoomAlias(ctx, request.Alias, request.RoomID, string(request.SenderID)); err != nil {
 		return err
 	}
 
diff --git a/roomserver/internal/perform/perform_create_room.go b/roomserver/internal/perform/perform_create_room.go
index 12e756c2e..247a5bcd4 100644
--- a/roomserver/internal/perform/perform_create_room.go
+++ b/roomserver/internal/perform/perform_create_room.go
@@ -434,9 +434,9 @@ func (c *Creator) PerformCreateRoom(ctx context.Context, userID spec.UserID, roo
 	// been taken.
 	if roomAlias != "" {
 		aliasReq := api.SetRoomAliasRequest{
-			Alias:  roomAlias,
-			RoomID: roomID.String(),
-			UserID: userID.String(),
+			SenderID: senderID,
+			Alias:    roomAlias,
+			RoomID:   roomID.String(),
 		}
 
 		var aliasResp api.SetRoomAliasResponse
diff --git a/roomserver/internal/perform/perform_upgrade.go b/roomserver/internal/perform/perform_upgrade.go
index 32f547dc1..ff0464c58 100644
--- a/roomserver/internal/perform/perform_upgrade.go
+++ b/roomserver/internal/perform/perform_upgrade.go
@@ -188,7 +188,7 @@ func moveLocalAliases(ctx context.Context,
 			return fmt.Errorf("Failed to remove old room alias: %w", err)
 		}
 
-		setAliasReq := api.SetRoomAliasRequest{UserID: userID.String(), Alias: alias, RoomID: newRoomID}
+		setAliasReq := api.SetRoomAliasRequest{SenderID: senderID, Alias: alias, RoomID: newRoomID}
 		setAliasRes := api.SetRoomAliasResponse{}
 		if err = URSAPI.SetRoomAlias(ctx, &setAliasReq, &setAliasRes); err != nil {
 			return fmt.Errorf("Failed to set new room alias: %w", err)
diff --git a/roomserver/roomserver_test.go b/roomserver/roomserver_test.go
index ce0721bea..d24a31f61 100644
--- a/roomserver/roomserver_test.go
+++ b/roomserver/roomserver_test.go
@@ -274,9 +274,8 @@ func TestPurgeRoom(t *testing.T) {
 		if !isPublished {
 			t.Fatalf("room should be published before purging")
 		}
-
 		aliasResp := &api.SetRoomAliasResponse{}
-		if err = rsAPI.SetRoomAlias(ctx, &api.SetRoomAliasRequest{RoomID: room.ID, Alias: "myalias", UserID: alice.ID}, aliasResp); err != nil {
+		if err = rsAPI.SetRoomAlias(ctx, &api.SetRoomAliasRequest{RoomID: room.ID, Alias: "myalias", SenderID: spec.SenderID(alice.ID)}, aliasResp); err != nil {
 			t.Fatal(err)
 		}
 		// check the alias is actually there