diff --git a/src/matrix/storage/common.ts b/src/matrix/storage/common.ts
index 926ccbbf..8d2dd2d2 100644
--- a/src/matrix/storage/common.ts
+++ b/src/matrix/storage/common.ts
@@ -42,9 +42,9 @@ export const STORE_MAP: Readonly<{ [name : string]: string }> = Object.freeze(ST
 
 export class StorageError extends Error {
     errcode?: string;
-    cause?: Error;
+    cause: Error | null;
 
-    constructor(message: string, cause?: Error) {
+    constructor(message: string, cause: Error | null = null) {
         super(message);
         if (cause) {
             this.errcode = cause.name;
diff --git a/src/matrix/storage/idb/error.ts b/src/matrix/storage/idb/error.ts
index 02953886..1c6875fb 100644
--- a/src/matrix/storage/idb/error.ts
+++ b/src/matrix/storage/idb/error.ts
@@ -21,7 +21,7 @@ export class IDBError extends StorageError {
     storeName: string;
     databaseName: string;
 
-    constructor(message: string, source, cause: DOMException | null) {
+    constructor(message: string, source, cause: DOMException | null = null) {
         const storeName = source?.name || "<unknown store>";
         const databaseName = source?.transaction?.db?.name || "<unknown db>";
         let fullMessage = `${message} on ${databaseName}.${storeName}`;
@@ -37,7 +37,7 @@ export class IDBError extends StorageError {
         if (cause) {
             fullMessage += cause.message;
         }
-        super(fullMessage, cause || undefined);
+        super(fullMessage, cause);
         this.storeName = storeName;
         this.databaseName = databaseName;
     }