diff --git a/keyserver/src/updaters/olm-session-updater.js b/keyserver/src/updaters/olm-session-updater.js
--- a/keyserver/src/updaters/olm-session-updater.js
+++ b/keyserver/src/updaters/olm-session-updater.js
@@ -1,13 +1,13 @@
 // @flow
 
-import type { EncryptResult } from '@commapp/olm';
+import type { EncryptResult, Session as OlmSession } from '@commapp/olm';
 
 import { ServerError } from 'lib/utils/errors.js';
 import sleep from 'lib/utils/sleep.js';
 
 import { SQL, dbQuery } from '../database/database.js';
 import { fetchPickledOlmAccount } from '../fetchers/olm-account-fetchers.js';
-import { unpickleOlmSession } from '../utils/olm-utils.js';
+import { unpickleSessionAndUseCallback } from '../utils/olm-objects.js';
 
 const maxOlmSessionUpdateAttemptTime = 30000;
 const olmSessionUpdateRetryDelay = 50;
@@ -45,21 +45,28 @@
     }
 
     const [{ version, pickled_olm_session: pickledSession }] = olmSessionResult;
-    const session = await unpickleOlmSession(pickledSession, picklingKey);
 
     const encryptedMessages: { [string]: EncryptResult } = {};
-    for (const messageName in messagesToEncrypt) {
-      encryptedMessages[messageName] = session.encrypt(
-        messagesToEncrypt[messageName],
-      );
-    }
+    const {
+      pickledOlmSession: { pickledSession: updatedSession },
+    } = await unpickleSessionAndUseCallback(
+      {
+        picklingKey,
+        pickledSession,
+      },
+      (olmSession: OlmSession) => {
+        for (const messageName in messagesToEncrypt) {
+          encryptedMessages[messageName] = olmSession.encrypt(
+            messagesToEncrypt[messageName],
+          );
+        }
+      },
+    );
 
     if (dbPersistCondition && !dbPersistCondition(encryptedMessages)) {
       return { encryptedMessages, dbPersistConditionViolated: true };
     }
 
-    const updatedSession = session.pickle(picklingKey);
-
     const [transactionResult] = await dbQuery(
       SQL`
         START TRANSACTION;
diff --git a/keyserver/src/utils/olm-objects.js b/keyserver/src/utils/olm-objects.js
--- a/keyserver/src/utils/olm-objects.js
+++ b/keyserver/src/utils/olm-objects.js
@@ -1,6 +1,9 @@
 // @flow
 
-import olm, { type Account as OlmAccount } from '@commapp/olm';
+import olm, {
+  type Account as OlmAccount,
+  type Session as OlmSession,
+} from '@commapp/olm';
 import uuid from 'uuid';
 
 import { ServerError } from 'lib/utils/errors.js';
@@ -56,4 +59,42 @@
   };
 }
 
-export { unpickleAccountAndUseCallback, createPickledOlmAccount };
+export type PickledOlmSession = {
+  +picklingKey: string,
+  +pickledSession: string,
+};
+async function unpickleSessionAndUseCallback<T>(
+  pickledOlmSession: PickledOlmSession,
+  callback: (session: OlmSession, picklingKey: string) => Promise<T> | T,
+): Promise<{ +result: T, +pickledOlmSession: PickledOlmSession }> {
+  const { picklingKey, pickledSession } = pickledOlmSession;
+
+  await olm.init();
+
+  const session = new olm.Session();
+  session.unpickle(picklingKey, pickledSession);
+
+  let result;
+  try {
+    result = await callback(session, picklingKey);
+  } catch (e) {
+    throw new ServerError(getMessageForException(e) ?? 'unknown_error');
+  }
+  const updatedSession = session.pickle(picklingKey);
+
+  session.free();
+
+  return {
+    result,
+    pickledOlmSession: {
+      ...pickledOlmSession,
+      pickledSession: updatedSession,
+    },
+  };
+}
+
+export {
+  unpickleAccountAndUseCallback,
+  createPickledOlmAccount,
+  unpickleSessionAndUseCallback,
+};
diff --git a/keyserver/src/utils/olm-utils.js b/keyserver/src/utils/olm-utils.js
--- a/keyserver/src/utils/olm-utils.js
+++ b/keyserver/src/utils/olm-utils.js
@@ -1,9 +1,6 @@
 // @flow
 
-import type {
-  Account as OlmAccount,
-  Session as OlmSession,
-} from '@commapp/olm';
+import type { Account as OlmAccount } from '@commapp/olm';
 import olm from '@commapp/olm';
 import invariant from 'invariant';
 
@@ -48,16 +45,6 @@
   return session.pickle(accountPicklingKey);
 }
 
-async function unpickleOlmSession(
-  pickledSession: string,
-  picklingKey: string,
-): Promise<OlmSession> {
-  await olm.init();
-  const session = new olm.Session();
-  session.unpickle(picklingKey, pickledSession);
-  return session;
-}
-
 async function markPrekeysAsPublished(): Promise<void> {
   await Promise.all([
     fetchCallUpdateOlmAccount('content', (contentAccount: OlmAccount) => {
@@ -276,7 +263,6 @@
 
 export {
   createPickledOlmSession,
-  unpickleOlmSession,
   uploadNewOneTimeKeys,
   getContentSigningKey,
   validateAndUploadAccountPrekeys,