diff --git a/filegateway/session_pool.js b/filegateway/session_pool.js
index 678b69e..e237b38 100644
--- a/filegateway/session_pool.js
+++ b/filegateway/session_pool.js
@@ -55,13 +55,13 @@ class SessionPool {
   /**
    * Cleans up expired sessions from the pool.
    */
-  cleanupSessions() {
+  async cleanupSessions() {
     const now = Date.now();
 
     for (const [key, session] of this.sessions) {
       if (session.expiration <= now) {
         this.sessions.delete(key);
-        session.off(session.value)
+        await session.off(session.value)
       }
     }
   }