diff --git a/readme.MD b/readme.MD
index 716f5c0..d3bb3e7 100644
--- a/readme.MD
+++ b/readme.MD
@@ -113,7 +113,7 @@ set OPENAI_API_BASE=https://my-super-proxy.vercel.app/v1
   - [x] `max_tokens`
   - [x] `n` (`candidateCount` <8) _n.b.: atm api does not accept >1_
   - [ ] `presence_penalty`
-  - [ ] `response_format`
+  - [x] `response_format`
   - [ ] `seed`
   - [x] `stop`: string|array (`stopSequences` [1,5])
   - [x] stream
diff --git a/src/worker.mjs b/src/worker.mjs
index 8c23947..365d13c 100644
--- a/src/worker.mjs
+++ b/src/worker.mjs
@@ -135,6 +135,9 @@ const transformConfig = (req) => {
       cfg[matchedKey] = req[key];
     }
   }
+  if (req.response_format?.type === "json_object") {
+    cfg.response_mime_type = "application/json";
+  }
   return cfg;
 };