diff --git a/o2web/source/o2_core/o2/xDesktop/Actions/RestActions.js b/o2web/source/o2_core/o2/xDesktop/Actions/RestActions.js
index 680893b1eccea92601cefbba290e48764f1c3e4d..00fa1d45451ba3626a4f0ca44e19f4181abfcb31 100644
--- a/o2web/source/o2_core/o2/xDesktop/Actions/RestActions.js
+++ b/o2web/source/o2_core/o2/xDesktop/Actions/RestActions.js
@@ -167,7 +167,7 @@ MWF.xDesktop.Actions.RestActions = new Class({
         xhr.open(method, uri, async!==false);
         xhr.withCredentials = true;
 
-        if (file) messageItem = this.addFormDataMessage(file, false, xhr, progress);
+        if (file && File.prototype.isPrototypeOf(file)) messageItem = this.addFormDataMessage(file, false, xhr, progress);
         xhr.send(data);
     },
     setMessageText: function(messageItem, text){