diff --git a/docs/HISTORY.txt b/docs/HISTORY.txt
index b9c0c26..413cbb3 100644
--- a/docs/HISTORY.txt
+++ b/docs/HISTORY.txt
@@ -4,6 +4,9 @@ Changelog
 1.0.6 (unreleased)
 ------------------
 
+* Avoid theming ajax response.
+  [elro]
+
 * Ensure context is a content item of some sort.
   [elro]
 
diff --git a/plone/formwidget/contenttree/widget.py b/plone/formwidget/contenttree/widget.py
index 6f5945c..d648f33 100644
--- a/plone/formwidget/contenttree/widget.py
+++ b/plone/formwidget/contenttree/widget.py
@@ -101,6 +101,8 @@ class Fetch(BrowserView):
                 newNode = strategy.decoratorFactory(newNode)
                 children.append(newNode)
 
+        self.request.response.setHeader('X-Theme-Disabled', 'True')
+
         return self.fragment_template(children=children, level=int(level))