diff --git a/src/matrix/storage/idb/QueryTarget.ts b/src/matrix/storage/idb/QueryTarget.ts
index e3b77810..c8fc8df1 100644
--- a/src/matrix/storage/idb/QueryTarget.ts
+++ b/src/matrix/storage/idb/QueryTarget.ts
@@ -31,9 +31,11 @@ interface QueryTargetInterface<T> {
 
 export class QueryTarget<T> {
     protected _target: QueryTargetInterface<T>;
+    protected _idbFactory: IDBFactory
 
-    constructor(target: QueryTargetInterface<T>) {
+    constructor(target: QueryTargetInterface<T>, idbFactory: IDBFactory) {
         this._target = target;
+        this._idbFactory = idbFactory;
     }
 
     _openCursor(range?: IDBQuery, direction?: IDBCursorDirection): IDBRequest<IDBCursorWithValue | null> {
@@ -155,7 +157,7 @@ export class QueryTarget<T> {
      */
     async findExistingKeys(keys: IDBValidKey[], backwards: boolean, callback: (key: IDBValidKey, found: boolean) => boolean): Promise<void> {
         const direction = backwards ? "prev" : "next";
-        const compareKeys = (a, b) => backwards ? -indexedDB.cmp(a, b) : indexedDB.cmp(a, b);
+        const compareKeys = (a, b) => backwards ? -this._idbFactory.cmp(a, b) : this._idbFactory.cmp(a, b);
         const sortedKeys = keys.slice().sort(compareKeys);
         const firstKey = backwards ? sortedKeys[sortedKeys.length - 1] : sortedKeys[0];
         const lastKey = backwards ? sortedKeys[0] : sortedKeys[sortedKeys.length - 1];
diff --git a/src/matrix/storage/idb/Storage.ts b/src/matrix/storage/idb/Storage.ts
index bffdb642..7e02c111 100644
--- a/src/matrix/storage/idb/Storage.ts
+++ b/src/matrix/storage/idb/Storage.ts
@@ -23,11 +23,13 @@ const WEBKITEARLYCLOSETXNBUG_BOGUS_KEY = "782rh281re38-boguskey";
 export class Storage {
     private _db: IDBDatabase;
     private _hasWebkitEarlyCloseTxnBug: boolean;
+    private _idbFactory: IDBFactory
     private _IDBKeyRange: typeof IDBKeyRange
     storeNames: typeof StoreNames;
 
-    constructor(idbDatabase: IDBDatabase, _IDBKeyRange: typeof IDBKeyRange, hasWebkitEarlyCloseTxnBug: boolean) {
+    constructor(idbDatabase: IDBDatabase, idbFactory: IDBFactory, _IDBKeyRange: typeof IDBKeyRange, hasWebkitEarlyCloseTxnBug: boolean) {
         this._db = idbDatabase;
+        this._idbFactory = idbFactory;
         this._IDBKeyRange = _IDBKeyRange;
         this._hasWebkitEarlyCloseTxnBug = hasWebkitEarlyCloseTxnBug;
         this.storeNames = StoreNames;
@@ -49,7 +51,7 @@ export class Storage {
             if (this._hasWebkitEarlyCloseTxnBug) {
                 await reqAsPromise(txn.objectStore(storeNames[0]).get(WEBKITEARLYCLOSETXNBUG_BOGUS_KEY));
             }
-            return new Transaction(txn, storeNames, this._IDBKeyRange);
+            return new Transaction(txn, storeNames, this._idbFactory, this._IDBKeyRange);
         } catch(err) {
             throw new StorageError("readTxn failed", err);
         }
@@ -64,7 +66,7 @@ export class Storage {
             if (this._hasWebkitEarlyCloseTxnBug) {
                 await reqAsPromise(txn.objectStore(storeNames[0]).get(WEBKITEARLYCLOSETXNBUG_BOGUS_KEY));
             }
-            return new Transaction(txn, storeNames, this._IDBKeyRange);
+            return new Transaction(txn, storeNames, this._idbFactory, this._IDBKeyRange);
         } catch(err) {
             throw new StorageError("readWriteTxn failed", err);
         }
diff --git a/src/matrix/storage/idb/StorageFactory.ts b/src/matrix/storage/idb/StorageFactory.ts
index 6db78c36..55e6f604 100644
--- a/src/matrix/storage/idb/StorageFactory.ts
+++ b/src/matrix/storage/idb/StorageFactory.ts
@@ -70,7 +70,7 @@ export class StorageFactory {
 
         const hasWebkitEarlyCloseTxnBug = await detectWebkitEarlyCloseTxnBug(this._idbFactory);
         const db = await openDatabaseWithSessionId(sessionId, this._idbFactory, log);
-        return new Storage(db, this._IDBKeyRange, hasWebkitEarlyCloseTxnBug);
+        return new Storage(db, this._idbFactory, this._IDBKeyRange, hasWebkitEarlyCloseTxnBug);
     }
 
     delete(sessionId: string): Promise<IDBDatabase> {
diff --git a/src/matrix/storage/idb/Store.ts b/src/matrix/storage/idb/Store.ts
index e2da0707..6dafd90e 100644
--- a/src/matrix/storage/idb/Store.ts
+++ b/src/matrix/storage/idb/Store.ts
@@ -130,8 +130,8 @@ class QueryTargetWrapper<T> {
 export class Store<T> extends QueryTarget<T> {
     private _transaction: Transaction;
 
-    constructor(idbStore: IDBObjectStore, transaction: Transaction) {
-        super(new QueryTargetWrapper<T>(idbStore));
+    constructor(idbStore: IDBObjectStore, transaction: Transaction, idbFactory: IDBFactory) {
+        super(new QueryTargetWrapper<T>(idbStore), idbFactory);
         this._transaction = transaction;
     }
 
@@ -145,7 +145,7 @@ export class Store<T> extends QueryTarget<T> {
     }
 
     index(indexName: string): QueryTarget<T> {
-        return new QueryTarget<T>(new QueryTargetWrapper<T>(this._idbStore.index(indexName)));
+        return new QueryTarget<T>(new QueryTargetWrapper<T>(this._idbStore.index(indexName)), this._idbFactory);
     }
 
     put(value: T): void {
diff --git a/src/matrix/storage/idb/Transaction.ts b/src/matrix/storage/idb/Transaction.ts
index ea21b745..1eaf0caf 100644
--- a/src/matrix/storage/idb/Transaction.ts
+++ b/src/matrix/storage/idb/Transaction.ts
@@ -40,13 +40,15 @@ export class Transaction {
     private _txn: IDBTransaction;
     private _allowedStoreNames: StoreNames[];
     private _stores: { [storeName in StoreNames]?: any };
+    idbFactory: IDBFactory
+    IDBKeyRange: typeof IDBKeyRange
 
-    constructor(txn: IDBTransaction, allowedStoreNames: StoreNames[], IDBKeyRange) {
+    constructor(txn: IDBTransaction, allowedStoreNames: StoreNames[], _idbFactory: IDBFactory, _IDBKeyRange: typeof IDBKeyRange) {
         this._txn = txn;
         this._allowedStoreNames = allowedStoreNames;
         this._stores = {};
-        // @ts-ignore
-        this.IDBKeyRange = IDBKeyRange;
+        this.idbFactory = _idbFactory;
+        this.IDBKeyRange = _IDBKeyRange;
     }
 
     _idbStore(name: StoreNames): Store<any> {
@@ -54,7 +56,7 @@ export class Transaction {
             // more specific error? this is a bug, so maybe not ...
             throw new StorageError(`Invalid store for transaction: ${name}, only ${this._allowedStoreNames.join(", ")} are allowed.`);
         }
-        return new Store(this._txn.objectStore(name), this);
+        return new Store(this._txn.objectStore(name), this, this.idbFactory);
     }
 
     _store<T>(name: StoreNames, mapStore: (idbStore: Store<any>) => T): T {