diff --git a/public/src/es.js b/public/src/es.js
index 524afd0c..a5f9ec3d 100644
--- a/public/src/es.js
+++ b/public/src/es.js
@@ -31,9 +31,20 @@ module.exports.send = function (method, path, data, server, disable_auth_alert)
   // delayed loading for circular references
   var settings = require("./settings");
 
+  let contentType;
+  if (data) {
+    try {
+      JSON.parse(data);
+      contentType = 'application/json';
+    } catch (e) {
+      contentType = 'text/plain';
+    }
+  }
+
   var options = {
     url: '../api/sense/proxy?uri=' + encodeURIComponent(path),
     data: method == "GET" ? null : data,
+    contentType,
     cache: false,
     crossDomain: true,
     type: method,