diff --git a/src/matrix/storage/common.js b/src/matrix/storage/common.js
index 473b8eb6..4a4060b2 100644
--- a/src/matrix/storage/common.js
+++ b/src/matrix/storage/common.js
@@ -27,6 +27,7 @@ export const STORE_NAMES = Object.freeze([
     "olmSessions",
     "inboundGroupSessions",
     "outboundGroupSessions",
+    "groupSessionDecryptions",
 ]);
 
 export const STORE_MAP = Object.freeze(STORE_NAMES.reduce((nameMap, name) => {
diff --git a/src/matrix/storage/idb/Transaction.js b/src/matrix/storage/idb/Transaction.js
index 8b42b0f7..946b06cc 100644
--- a/src/matrix/storage/idb/Transaction.js
+++ b/src/matrix/storage/idb/Transaction.js
@@ -29,6 +29,7 @@ import {DeviceIdentityStore} from "./stores/DeviceIdentityStore.js";
 import {OlmSessionStore} from "./stores/OlmSessionStore.js";
 import {InboundGroupSessionStore} from "./stores/InboundGroupSessionStore.js";
 import {OutboundGroupSessionStore} from "./stores/OutboundGroupSessionStore.js";
+import {GroupSessionDecryptionStore} from "./stores/GroupSessionDecryptionStore.js";
 
 export class Transaction {
     constructor(txn, allowedStoreNames) {
@@ -105,6 +106,11 @@ export class Transaction {
     get outboundGroupSessions() {
         return this._store("outboundGroupSessions", idbStore => new OutboundGroupSessionStore(idbStore));
     }
+
+    get groupSessionDecryptions() {
+        return this._store("groupSessionDecryptions", idbStore => new OutboundGroupSessionStore(idbStore));
+    }
+
     complete() {
         return txnAsPromise(this._txn);
     }
diff --git a/src/matrix/storage/idb/schema.js b/src/matrix/storage/idb/schema.js
index 2060cb39..63458916 100644
--- a/src/matrix/storage/idb/schema.js
+++ b/src/matrix/storage/idb/schema.js
@@ -13,6 +13,7 @@ export const schema = [
     createOlmSessionStore,
     createInboundGroupSessionsStore,
     createOutboundGroupSessionsStore,
+    createGroupSessionDecryptions,
 ];
 // TODO: how to deal with git merge conflicts of this array?
 
@@ -89,3 +90,7 @@ function createOutboundGroupSessionsStore(db) {
     db.createObjectStore("outboundGroupSessions", {keyPath: "roomId"});
 }
 
+//v8
+function createGroupSessionDecryptions(db) {
+    db.createObjectStore("groupSessionDecryptions", {keyPath: "key"});
+}
diff --git a/src/matrix/storage/idb/stores/GroupSessionDecryptionStore.js b/src/matrix/storage/idb/stores/GroupSessionDecryptionStore.js
new file mode 100644
index 00000000..299b1520
--- /dev/null
+++ b/src/matrix/storage/idb/stores/GroupSessionDecryptionStore.js
@@ -0,0 +1,34 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+function encodeKey(roomId, senderKey, sessionId) {
+    return `${roomId}|${senderKey}|${sessionId}`;
+}
+
+export class GroupSessionDecryptionStore {
+    constructor(store) {
+        this._store = store;
+    }
+
+    get(roomId, sessionId, messageIndex) {
+        return this._store.get(encodeKey(roomId, sessionId, messageIndex));
+    }
+
+    set(decryption) {
+        decryption.key = encodeKey(decryption.roomId, decryption.sessionId, decryption.messageIndex);
+        this._store.put(decryption);
+    }
+}
diff --git a/src/matrix/storage/idb/stores/InboundGroupSessionStore.js b/src/matrix/storage/idb/stores/InboundGroupSessionStore.js
index 3de5a103..d05c67ff 100644
--- a/src/matrix/storage/idb/stores/InboundGroupSessionStore.js
+++ b/src/matrix/storage/idb/stores/InboundGroupSessionStore.js
@@ -29,6 +29,10 @@ export class InboundGroupSessionStore {
         return key === fetchedKey;
     }
 
+    get(roomId, senderKey, sessionId) {
+        return this._store.get(encodeKey(roomId, senderKey, sessionId));
+    }
+
     set(session) {
         session.key = encodeKey(session.roomId, session.senderKey, session.sessionId);
         this._store.put(session);