diff --git a/src/github.com/matrix-org/dendrite/federationapi/writers/send.go b/src/github.com/matrix-org/dendrite/federationapi/writers/send.go
index 89acd5b9..c43196d7 100644
--- a/src/github.com/matrix-org/dendrite/federationapi/writers/send.go
+++ b/src/github.com/matrix-org/dendrite/federationapi/writers/send.go
@@ -113,7 +113,7 @@ func (t *txnReq) processTransaction() (*gomatrixserverlib.RespSend, error) {
 
 type unknownRoomError string
 
-func (e unknownRoomError) Error() string { return fmt.Sprintf("unknown room %q", e) }
+func (e unknownRoomError) Error() string { return fmt.Sprintf("unknown room %q", string(e)) }
 
 func (t *txnReq) processEvent(e gomatrixserverlib.Event) error {
 	refs := e.PrevEvents()