diff --git a/riak/transports/http.py b/riak/transports/http.py
index c77955b6..9e740de9 100644
--- a/riak/transports/http.py
+++ b/riak/transports/http.py
@@ -236,7 +236,8 @@ def mapred(self, inputs, query, timeout=None):
 
         # Do the request...
         url = "/" + self._mapred_prefix
-        response = self.http_request('POST', url, {}, content)
+        headers = {'Content-Type': 'application/json'}
+        response = self.http_request('POST', url, headers, content)
 
         # Make sure the expected status code came back...
         status = response[0]['http_code']