diff --git a/src/core.ts b/src/core.ts
index 59796bb..abb0b6d 100644
--- a/src/core.ts
+++ b/src/core.ts
@@ -395,7 +395,7 @@ export abstract class APIClient {
       !headers ? {}
       : Symbol.iterator in headers ?
         Object.fromEntries(Array.from(headers as Iterable<string[]>).map((header) => [...header]))
-      : { ...headers }
+      : { ...(headers as any as Record<string, string>) }
     );
   }