diff --git a/src/github.com/matrix-org/dendrite/clientapi/writers/membership.go b/src/github.com/matrix-org/dendrite/clientapi/writers/membership.go
index 32f769974..b73d4ab28 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/writers/membership.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/writers/membership.go
@@ -39,7 +39,12 @@ func SendMembership(
 	roomID string, membership string, cfg config.Dendrite,
 	queryAPI api.RoomserverQueryAPI, producer *producers.RoomserverProducer,
 ) util.JSONResponse {
-	localpart, _, err := gomatrixserverlib.SplitID('@', device.UserID)
+	stateKey, reason, reqErr := getMembershipStateKey(req, device, membership)
+	if reqErr != nil {
+		return *reqErr
+	}
+
+	localpart, _, err := gomatrixserverlib.SplitID('@', stateKey)
 	if err != nil {
 		return httputil.LogThenError(req, err)
 	}
@@ -49,11 +54,6 @@ func SendMembership(
 		return httputil.LogThenError(req, err)
 	}
 
-	stateKey, reason, reqErr := getMembershipStateKey(req, device, membership)
-	if reqErr != nil {
-		return *reqErr
-	}
-
 	builder := gomatrixserverlib.EventBuilder{
 		Sender:   device.UserID,
 		RoomID:   roomID,