diff --git a/src/matrix/e2ee/megolm/decryption/DecryptionChanges.js b/src/matrix/e2ee/megolm/decryption/DecryptionChanges.js
index 5597aaf7..10a2da87 100644
--- a/src/matrix/e2ee/megolm/decryption/DecryptionChanges.js
+++ b/src/matrix/e2ee/megolm/decryption/DecryptionChanges.js
@@ -66,10 +66,7 @@ export class DecryptionChanges {
         }
 
         if (!decryption) {
-            txn.groupSessionDecryptions.set({
-                roomId,
-                sessionId,
-                messageIndex,
+            txn.groupSessionDecryptions.set(roomId, sessionId, messageIndex, {
                 eventId,
                 timestamp
             });
diff --git a/src/matrix/storage/idb/stores/GroupSessionDecryptionStore.js b/src/matrix/storage/idb/stores/GroupSessionDecryptionStore.js
index 99ededb9..8f8df3e7 100644
--- a/src/matrix/storage/idb/stores/GroupSessionDecryptionStore.js
+++ b/src/matrix/storage/idb/stores/GroupSessionDecryptionStore.js
@@ -27,8 +27,8 @@ export class GroupSessionDecryptionStore {
         return this._store.get(encodeKey(roomId, sessionId, messageIndex));
     }
 
-    set(decryption) {
-        decryption.key = encodeKey(decryption.roomId, decryption.sessionId, decryption.messageIndex);
+    set(roomId, sessionId, messageIndex, decryption) {
+        decryption.key = encodeKey(roomId, sessionId, messageIndex);
         this._store.put(decryption);
     }
 }