diff --git a/federationapi/routing/join.go b/federationapi/routing/join.go
index 2fcb929ad..875f0e067 100644
--- a/federationapi/routing/join.go
+++ b/federationapi/routing/join.go
@@ -17,6 +17,7 @@ package routing
 import (
 	"encoding/json"
 	"net/http"
+	"strconv"
 	"time"
 
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
@@ -102,7 +103,7 @@ func MakeJoin(
 		Code: http.StatusOK,
 		JSON: map[string]interface{}{
 			"event":        builder,
-			"room_version": vQueryRes.RoomVersion,
+			"room_version": strconv.Itoa(vQueryRes.RoomVersion),
 		},
 	}
 }