diff --git a/lib/makeRequest.js b/lib/makeRequest.js
index <HASH>..<HASH> 100644
--- a/lib/makeRequest.js
+++ b/lib/makeRequest.js
@@ -55,7 +55,7 @@ function getRequestOpts(self, requestArgs, spec, overrideData) {
 
   // Pull request data and options (headers, auth) from args.
   var dataFromArgs = utils.getDataFromArgs(args);
-  var data = encode(Object.assign(dataFromArgs, overrideData));
+  var data = encode(Object.assign({}, dataFromArgs, overrideData));
   var options = utils.getOptionsFromArgs(args);
 
   // Validate that there are no more args.
Do not mutate data param in general (shallow)