diff --git a/federationapi/routing/send.go b/federationapi/routing/send.go
index bde6729df..df0aebc11 100644
--- a/federationapi/routing/send.go
+++ b/federationapi/routing/send.go
@@ -279,6 +279,7 @@ func (t *txnReq) processEDUs(edus []gomatrixserverlib.EDU) {
 			}
 			for userID, byUser := range directPayload.Messages {
 				for deviceID, message := range byUser {
+					// TODO: check that the user and the device actually exist here
 					if err := t.eduProducer.SendToDevice(t.context, userID, deviceID, directPayload.EventType, message); err != nil {
 						util.GetLogger(t.context).WithError(err).Error("Failed to send send-to-device event to edu server")
 					}
diff --git a/syncapi/storage/storage_test.go b/syncapi/storage/storage_test.go
index 88efd8f04..184bbdda5 100644
--- a/syncapi/storage/storage_test.go
+++ b/syncapi/storage/storage_test.go
@@ -539,7 +539,8 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 	}
 
 	// At this point we should get exactly one message. We're sending the sync position
-	// that we were given from the update.
+	// that we were given from the update and the send-to-device update will be updated
+	// in the database to reflect that this was the sync position we sent the message at.
 	second, err := db.SendToDeviceUpdatesForSync(ctx, "alice", "one", types.NewStreamToken(0, streamPos))
 	if err != nil {
 		t.Fatal(err)
@@ -560,7 +561,7 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 	}
 
 	// At this point we should now have no updates, because we've progressed the sync
-	// position. Therefore the update from before will be cleane
+	// position. Therefore the update from before will not be sent again.
 	fourth, err := db.SendToDeviceUpdatesForSync(ctx, "alice", "one", types.NewStreamToken(0, streamPos+1))
 	if err != nil {
 		t.Fatal(err)
@@ -569,6 +570,8 @@ func TestSendToDeviceBehaviour(t *testing.T) {
 		t.Fatal("fourth call should have no updates")
 	}
 
+	// At this point we should still have no updates, because no new updates have been
+	// sent.
 	fifth, err := db.SendToDeviceUpdatesForSync(ctx, "alice", "one", types.NewStreamToken(0, streamPos+2))
 	if err != nil {
 		t.Fatal(err)