diff --git a/web/shared-worker/worker/worker-crypto.js b/web/shared-worker/worker/worker-crypto.js
--- a/web/shared-worker/worker/worker-crypto.js
+++ b/web/shared-worker/worker/worker-crypto.js
@@ -181,6 +181,8 @@
   } = notificationAccountWithPicklingKey;
 
   const notificationsPrekey = notificationsInitializationInfo.prekey;
+
+  // Memory is freed below after persisting.
   const session = new olm.Session();
   if (notificationsInitializationInfo.oneTimeKey) {
     session.create_outbound(
@@ -231,6 +233,7 @@
   });
 
   notificationAccount.free();
+  session.free();
 
   return { message, messageType };
 }