diff --git a/roomserver/api/canonical_alias.go b/roomserver/api/canonical_alias.go
new file mode 100644
index 000000000..c0f3b02e6
--- /dev/null
+++ b/roomserver/api/canonical_alias.go
@@ -0,0 +1,185 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package api
+
+import (
+	"context"
+	"net/http"
+
+	commonHTTP "github.com/matrix-org/dendrite/common/http"
+	opentracing "github.com/opentracing/opentracing-go"
+)
+
+// SetRoomCanonicalAliasRequest is a request to SetRoomCanonicalAlias
+type SetRoomCanonicalAliasRequest struct {
+	// ID of the user setting the alias
+	UserID string `json:"user_id"`
+	// New alias for the room
+	CanonicalAlias string `json:"alias"`
+	// The room ID the alias is referring to
+	RoomID string `json:"room_id"`
+}
+
+// SetRoomCanonicalAliasResponse is a response to SetRoomCanonicalAlias
+type SetRoomCanonicalAliasResponse struct {
+	// Does the alias already refer to a room?
+	AliasExists bool `json:"alias_exists"`
+	// Does the alias refer to a different room?
+	DifferentRoom bool `json:"different_room"`
+}
+
+// GetRoomIDForCanonicalAliasRequest is a request to GetRoomIDForCanonicalAlias
+type GetRoomIDForCanonicalAliasRequest struct {
+	// Canonical Alias we want to lookup
+	CanonicalAlias string `json:"alias"`
+}
+
+// GetRoomIDForCanonicalAliasResponse is a response to GetRoomIDForCanonicalAlias
+type GetRoomIDForCanonicalAliasResponse struct {
+	// The room ID the canonical alias refers to
+	RoomID string `json:"room_id"`
+}
+
+// GetCanonicalAliasForRoomIDRequest is a request to GetCanonicalAliasForRoomID
+type GetCanonicalAliasForRoomIDRequest struct {
+	// The room ID we want to find the canonical for
+	RoomID string `json:"room_id"`
+}
+
+// GetCanonicalForRoomIDResponse is a response to GetCanonicalAliasForRoomID
+type GetCanonicalAliasForRoomIDResponse struct {
+	CanonicalAlias string `json:"alias"`
+}
+
+// GetCreatorIDForCanonicalAliasRequest is a request to GetCreatorIDForCanonicalAlias
+type GetCreatorIDForCanonicalAliasRequest struct {
+	// The alias we want to find the creator of
+	CanonicalAlias string `json:"alias"`
+}
+
+// GetCreatorIDForCanonicalAliasResponse is a response to GetCreatorIDForCanonicalAlias
+type GetCreatorIDForAliasResponse struct {
+	// The user ID of the canonical alias creator
+	UserID string `json:"user_id"`
+}
+
+// RoomserverCanonicalAliasAPI is used to save, lookup or remove a room alias
+type RoomserverCanonicalAliasAPI interface {
+	// Set the room canonical alias
+	SetRoomCanonicalAlias(
+		ctx context.Context,
+		req *SetRoomCanonicalAliasRequest,
+		response *SetRoomCanonicalAliasResponse,
+	) error
+
+	// Get the room ID for an alias
+	GetRoomIDForCanonicalAlias(
+		ctx context.Context,
+		req *GetRoomIDForCanonicalAliasRequest,
+		response *GetRoomIDForCanonicalAliasResponse,
+	) error
+
+	// Get the canonical alias for a room ID
+	GetCanonicalAliasForRoomID(
+		ctx context.Context,
+		req *GetCanonicalAliasForRoomIDRequest,
+		response *GetCanonicalAliasForRoomIDResponse,
+	) error
+
+	// Get the user ID of the creator of a canonical alias
+	GetCreatorIDForCanonicalAlias(
+		ctx context.Context,
+		req *GetCreatorIDForCanonicalAliasRequest,
+		response *GetCreatorIDForCanonicalAliasAliasResponse,
+	) error
+}
+
+// RoomserverSetRoomCanonicalAliasPath is the HTTP path for the SetRoomCanonicalAlias API.
+const RoomserverSetRoomCanonicalAliasPath = "/api/roomserver/setRoomCanonicalAlias"
+
+// RoomserverGetRoomIDForCanonicalAliasPath is the HTTP path for the GetRoomIDForCanonicalAlias API.
+const RoomserverGetRoomIDForCanonicalAliasPath = "/api/roomserver/GetRoomIDForCanonicalAlias"
+
+// RoomserverGetCanonicalAliasForRoomIDPath is the HTTP path for the GetCanonicalAliasForRoomID API.
+const RoomserverGetCanonicalAliasForRoomIDPath = "/api/roomserver/GetCanonicalAliasForRoomID"
+
+// RoomserverGetCreatorIDForCanonicalAliasPath is the HTTP path for the GetCreatorIDForCanonicalAlias API.
+const RoomserverGetCreatorIDForCanonicalAliasPath = "/api/roomserver/GetCreatorIDForCanonicalAlias"
+
+// NewRoomserverCanonicalAliasAPIHTTP creates a RoomserverCanonicalAliasAPI implemented by talking to a HTTP POST API.
+// If httpClient is nil then it uses the http.DefaultClient
+func NewRoomserverCanonicalAliasAPIHTTP(roomserverURL string, httpClient *http.Client) RoomserverCanonicalAliasAPI {
+	if httpClient == nil {
+		httpClient = http.DefaultClient
+	}
+	return &httpRoomserverCanonicalAliasAPI{roomserverURL, httpClient}
+}
+
+type httpRoomserverCanonicalAliasAPI struct {
+	roomserverURL string
+	httpClient    *http.Client
+}
+
+// SetRoomCanonicalAlias implements RoomserverCanonicalAliasAPI
+func (h *httpRoomserverCanonicalAliasAPI) SetRoomCanonicalAlias(
+	ctx context.Context,
+	request *SetRoomCanonicalAliasRequest,
+	response *SetRoomCanonicalAliasResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "SetRoomCanonicalAlias")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverSetRoomCanonicalAliasPath
+	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
+
+// GetRoomIDForCanonicalAlias implements RoomserverCanonicalAliasAPI
+func (h *httpRoomserverCanonicalAliasAPI) GetRoomIDForCanonicalAlias(
+	ctx context.Context,
+	request *GetRoomIDForCanonicalAliasRequest,
+	response *GetRoomIDForCanonicalAliasResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "GetRoomIDForCanonicalAlias")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverGetRoomIDForCanonicalAliasPath
+	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
+
+// GetCanonicalAliasForRoomID implements RoomserverCanonicalAliasAPI
+func (h *httpRoomserverCanonicalAliasAPI) GetCanonicalAliasForRoomID(
+	ctx context.Context,
+	request *GetCanonicalAliasForRoomIDRequest,
+	response *GetCanonicalAliasForRoomIDResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "GetCanonicalAliasForRoomID")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverGetCanonicalAliasForRoomIDPath
+	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
+
+// GetCreatorIDForAlias implements RoomserverCanonicalAliasAPI
+func (h *httpRoomserverCanonicalAliasAPI) GetCreatorIDForCanonicalAlias(
+	ctx context.Context,
+	request *GetCreatorIDForCanonicalAliasRequest,
+	response *GetCreatorIDForCanonicalAliasResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "GetCreatorIDForCanonicalAlias")
+	defer span.Finish()
+
+	apiURL := h.roomserverURL + RoomserverGetCreatorIDForCanonicalAliasPath
+	return commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}
diff --git a/roomserver/canonical_alias/canonical_alias.go b/roomserver/canonical_alias/canonical_alias.go
index b129588eb..30b5c1a53 100644
--- a/roomserver/canonical_alias/canonical_alias.go
+++ b/roomserver/canonical_alias/canonical_alias.go
@@ -84,11 +84,11 @@ func (r *RoomserverCanonicalAliasAPI) SetRoomAlias(
 	// The alias belongs to a different room
 	if roomID != request.roomID {
 		// RFC: Is there a standard bool for wrong room?
-		response.CorrectRoom = false
+		response.DifferentRoom = true
 		return nil
 	}
 
-	response.CorrectRoom = true
+	response.DifferentRoom = false
 
 	// Save the new canonical alias
 	if err := r.DB.SetRoomCanonicalAlias(ctx, request.CanonicalAlias, request.RoomID, request.UserID); err != nil {