diff --git a/src/types.ts b/src/types.ts
index 7ee483f6..738d0051 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -7,7 +7,7 @@ export type JsonValue =
   | JsonArray;
 
 export type JsonObject = {
-  [key: string]: JsonValue;
+  [key: string]: JsonValue | undefined;
 };
 
 export type JsonArray = JsonValue[];