diff --git a/src/matrix/storage/idb/error.ts b/src/matrix/storage/idb/error.ts
index bd3fb0a8..0d723837 100644
--- a/src/matrix/storage/idb/error.ts
+++ b/src/matrix/storage/idb/error.ts
@@ -33,15 +33,10 @@ export class IDBError extends StorageError {
     storeName: string;
     databaseName: string;
 
-    constructor(message: string, source: IDBIndex | IDBCursor | IDBObjectStore, cause: DOMException | null = null) {
-        let storeName: string, databaseName: string;
-        if (source instanceof IDBCursor) {
-            storeName = _sourceName(source.source);
-            databaseName = _sourceDatabase(source.source);
-        } else {
-            storeName = _sourceName(source);
-            databaseName = _sourceDatabase(source);
-        }
+    constructor(message: string, sourceOrCursor: IDBIndex | IDBCursor | IDBObjectStore, cause: DOMException | null = null) {
+        const source = "source" in sourceOrCursor ? sourceOrCursor.source : sourceOrCursor;
+        const storeName = _sourceName(source);
+        const databaseName = _sourceDatabase(source);
         let fullMessage = `${message} on ${databaseName}.${storeName}`;
         if (cause) {
             fullMessage += ": ";