diff --git a/src/matrix/e2ee/RoomEncryption.js b/src/matrix/e2ee/RoomEncryption.js
index 69a93e57..bc17fa09 100644
--- a/src/matrix/e2ee/RoomEncryption.js
+++ b/src/matrix/e2ee/RoomEncryption.js
@@ -377,6 +377,8 @@ export class RoomEncryption {
 
     dispose() {
         this._disposed = true;
+        this._megolmBackfillCache.dispose();
+        this._megolmSyncCache.dispose();
     }
 }