diff --git a/src/matrix/Session.js b/src/matrix/Session.js
index 503ec3a5..2752fca7 100644
--- a/src/matrix/Session.js
+++ b/src/matrix/Session.js
@@ -301,7 +301,7 @@ export function tests() {
                     }
                 }
             };
-            const newSessionData = session.writeSync("b", 6, {}, syncTxn);
+            const newSessionData = await session.writeSync({next_batch: "b"}, 6, {}, syncTxn);
             assert(syncSet);
             assert.equal(session.syncToken, "a");
             assert.equal(session.syncFilterId, 5);