diff --git a/lib/nano.js b/lib/nano.js
index <HASH>..<HASH> 100644
--- a/lib/nano.js
+++ b/lib/nano.js
@@ -554,7 +554,7 @@ module.exports = exports = nano = function dbScope(cfg) {
           follows: true,
           length: Buffer.isBuffer(att.data) ?
             att.data.length : Buffer.byteLength(att.data),
-          content_type: att.contentType
+          'content_type': att.contentType
         };
         multipart.push({body: att.data});
       });
Fixes codestyle from #<I>