diff --git a/packages/api-client/src/client.ts b/packages/api-client/src/client.ts
index d55141e5..82309665 100644
--- a/packages/api-client/src/client.ts
+++ b/packages/api-client/src/client.ts
@@ -42,9 +42,10 @@ export function createApiClient(config: ApiClientConfig): ApiClient {
   function buildHeaders(options?: RequestInit): HeadersInit {
     const headers: Record<string, string> = {
       'Content-Type': 'application/json',
-      'x-request-id': typeof globalThis.crypto?.randomUUID === 'function'
-        ? globalThis.crypto.randomUUID()
-        : `${Date.now()}-${Math.random().toString(36).slice(2, 10)}`,
+      'x-request-id':
+        typeof globalThis.crypto?.randomUUID === 'function'
+          ? globalThis.crypto.randomUUID()
+          : `${Date.now()}-${Math.random().toString(36).slice(2, 10)}`,
       ...defaultHeaders,
     };
 
@@ -56,12 +57,16 @@ export function createApiClient(config: ApiClientConfig): ApiClient {
     }
 
     if (options?.headers) {
-      const extra =
-        options.headers instanceof Headers
-          ? Object.fromEntries(options.headers as any)
-          : Array.isArray(options.headers)
-            ? Object.fromEntries(options.headers)
-            : (options.headers as Record<string, string>);
+      const extra: Record<string, string> = {};
+      if (options.headers instanceof Headers) {
+        options.headers.forEach((value, key) => {
+          extra[key] = value;
+        });
+      } else if (Array.isArray(options.headers)) {
+        Object.assign(extra, Object.fromEntries(options.headers));
+      } else {
+        Object.assign(extra, options.headers);
+      }
       Object.assign(headers, extra);
     }