diff --git a/rauth/oauth.py b/rauth/oauth.py
index 5dc44b1..9988e16 100644
--- a/rauth/oauth.py
+++ b/rauth/oauth.py
@@ -66,7 +66,7 @@ def _normalize_request_parameters(self, oauth_params, req_kwargs):
         normalized = []
 
         params = req_kwargs.get('params', {})
-        data = req_kwargs.get('data', {})
+        data = req_kwargs.get('data', 'json')
         headers = req_kwargs.get('headers', {})
 
         # process request parameters