diff --git a/lib/bun_wrapper.js b/lib/bun_wrapper.js
index 6fe38a2c..555c41da 100644
--- a/lib/bun_wrapper.js
+++ b/lib/bun_wrapper.js
@@ -117,6 +117,7 @@ const wrapper = (handler, parsers) => {
       response = result
     }
     if (response instanceof Object && typeof response !== 'string' && !Buffer.isBuffer(response)) {
+      headers['Content-Type'] = 'application/json'
       response = JSON.stringify(response)
     }
     return new Response(response, { status: status, headers: headers })