_tJsx returns a React Object, the sub fn must return a React Object

not a string

src/components/views/login/CaptchaForm.js

@@ -17,6 +17,7 @@ limitations under the License.
 'use strict';
 
 import React from 'react';
+import ReactDOM from 'react-dom';
 import { _t, _tJsx } from '../../../languageHandler';
 
 var DIV_ID = 'mx_recaptcha';
@@ -66,11 +67,10 @@ module.exports = React.createClass({
                 // * jumping straight to a hosted captcha page (but we don't support that yet)
                 // * embedding the captcha in an iframe (if that works)
                 // * using a better captcha lib
-                warning.innerHTML = _tJsx(
-                     "Robot check is currently unavailable on desktop - please use a <a>web browser</a>",
-                     /<a>(.*?)<\/a>/,
-                     (sub) => { return "<a href='https://riot.im/app'>{ sub }</a>"; }
-                 );
+                ReactDOM.render(_tJsx(
+                    "Robot check is currently unavailable on desktop - please use a <a>web browser</a>",
+                    /<a>(.*?)<\/a>/,
+                    (sub) => { return <a href='https://riot.im/app'>{ sub }</a>; }), warning);
                 this.refs.recaptchaContainer.appendChild(warning);
             }
             else {