diff --git a/src/github.com/matrix-org/dendrite/roomserver/api/query.go b/src/github.com/matrix-org/dendrite/roomserver/api/query.go
index 248850bff..36961d383 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/api/query.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/api/query.go
@@ -21,10 +21,9 @@ import (
 	"fmt"
 	"net/http"
 
+	opentracing "github.com/opentracing/opentracing-go"
 	"github.com/opentracing/opentracing-go/ext"
 
-	"github.com/opentracing/opentracing-go"
-
 	"github.com/matrix-org/gomatrixserverlib"
 )
 
@@ -155,6 +154,18 @@ type QueryServerAllowedToSeeEventResponse struct {
 	AllowedToSeeEvent bool `json:"can_see_event"`
 }
 
+// QueryReserveRoomIDRequest is a request to QueryServerAllowedToSeeEvent
+type QueryReserveRoomIDRequest struct {
+	// TODO: Docs
+	RoomID string `json:"room_id"`
+}
+
+// QueryReserveRoomIDResponse is a response to QueryServerAllowedToSeeEvent
+type QueryReserveRoomIDResponse struct {
+	// TODO: Docs
+	Success bool `json:"success"`
+}
+
 // RoomserverQueryAPI is used to query information from the room server.
 type RoomserverQueryAPI interface {
 	// Query the latest events and state for a room from the room server.
@@ -218,6 +229,9 @@ const RoomserverQueryInvitesForUserPath = "/api/roomserver/queryInvitesForUser"
 // RoomserverQueryServerAllowedToSeeEventPath is the HTTP path for the QueryServerAllowedToSeeEvent API
 const RoomserverQueryServerAllowedToSeeEventPath = "/api/roomserver/queryServerAllowedToSeeEvent"
 
+// RoomserverQueryReserveRoomIDPath is the HTTP path for the QueryReserveRoomID API
+const RoomserverQueryReserveRoomIDPath = "/api/roomserver/queryReserveRoomID"
+
 // NewRoomserverQueryAPIHTTP creates a RoomserverQueryAPI implemented by talking to a HTTP POST API.
 // If httpClient is nil then it uses the http.DefaultClient
 func NewRoomserverQueryAPIHTTP(roomserverURL string, httpClient *http.Client) RoomserverQueryAPI {
@@ -310,6 +324,19 @@ func (h *httpRoomserverQueryAPI) QueryServerAllowedToSeeEvent(
 	return postJSON(ctx, span, h.httpClient, apiURL, request, response)
 }
 
+// TODO: Docs
+func (h *httpRoomserverQueryAPI) QueryReserveRoomID(
+	ctx context.Context,
+	request *QueryReserveRoomIDRequest,
+	response *QueryReserveRoomIDResponse,
+) (err error) {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "QueryReserveRoomID")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverQueryReserveRoomIDPath
+	return postJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
+
 func postJSON(
 	ctx context.Context, span opentracing.Span, httpClient *http.Client,
 	apiURL string, request, response interface{},
diff --git a/src/github.com/matrix-org/dendrite/roomserver/query/query.go b/src/github.com/matrix-org/dendrite/roomserver/query/query.go
index 265e4ad3d..c897a9b4e 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/query/query.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/query/query.go
@@ -418,6 +418,23 @@ func (r *RoomserverQueryAPI) QueryServerAllowedToSeeEvent(
 	return nil
 }
 
+// QueryReserveRoomID implements api.RoomserverQueryAPI
+func (r *RoomserverQueryAPI) QueryReserveRoomID(
+	ctx context.Context,
+	request *api.QueryReserveRoomIDRequest,
+	response *api.QueryReserveRoomIDResponse,
+) error {
+	nid, err := r.DB.RoomNID(ctx, request.RoomID)
+	if nid != 0 {
+		response.Success = false
+		return nil
+	}
+
+	response.Success = true
+
+	return err
+}
+
 // SetupHTTP adds the RoomserverQueryAPI handlers to the http.ServeMux.
 // nolint: gocyclo
 func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
@@ -505,4 +522,18 @@ func (r *RoomserverQueryAPI) SetupHTTP(servMux *http.ServeMux) {
 			return util.JSONResponse{Code: 200, JSON: &response}
 		}),
 	)
+	servMux.Handle(
+		api.RoomserverQueryReserveRoomIDPath,
+		common.MakeInternalAPI("queryReserveRoomID", func(req *http.Request) util.JSONResponse {
+			var request api.QueryReserveRoomIDRequest
+			var response api.QueryReserveRoomIDResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.ErrorResponse(err)
+			}
+			if err := r.QueryReserveRoomID(req.Context(), &request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: 200, JSON: &response}
+		}),
+	)
 }