diff --git a/src/github.com/matrix-org/dendrite/clientapi/readers/directory.go b/src/github.com/matrix-org/dendrite/clientapi/readers/directory.go
index 147a1c63d..4c25a45cd 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/readers/directory.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/readers/directory.go
@@ -27,10 +27,6 @@ import (
 	"github.com/matrix-org/util"
 )
 
-type roomID struct {
-	RoomID string `json:"room_id"`
-}
-
 // DirectoryRoom looks up a room alias
 func DirectoryRoom(
 	req *http.Request,
@@ -118,7 +114,9 @@ func SetLocalAlias(
 		}
 	}
 
-	var r roomID
+	var r struct {
+		RoomID string `json:"room_id"`
+	}
 	if resErr := httputil.UnmarshalJSONRequest(req, &r); resErr != nil {
 		return *resErr
 	}
diff --git a/src/github.com/matrix-org/dendrite/roomserver/storage/room_aliases_table.go b/src/github.com/matrix-org/dendrite/roomserver/storage/room_aliases_table.go
index a060a1b50..8b56b6d14 100644
--- a/src/github.com/matrix-org/dendrite/roomserver/storage/room_aliases_table.go
+++ b/src/github.com/matrix-org/dendrite/roomserver/storage/room_aliases_table.go
@@ -26,6 +26,8 @@ CREATE TABLE IF NOT EXISTS room_aliases (
     -- Room ID the alias refers to
     room_id TEXT NOT NULL
 );
+
+CREATE UNIQUE INDEX IF NOT EXISTS room_id_idx ON room_aliases(room_id);
 `
 
 const insertRoomAliasSQL = "" +