--- a/src/pyams_portal/zmi/portlet.py	Tue Sep 04 10:15:49 2018 +0200
+++ b/src/pyams_portal/zmi/portlet.py	Tue Sep 04 10:16:06 2018 +0200
@@ -127,6 +127,11 @@
 
     weight = 10
 
+    def updateWidgets(self, prefix=None):
+        super(PortletSettingsPropertiesEditor, self).updateWidgets(prefix)
+        if 'renderer' in self.widgets:
+            self.widgets['renderer'].required = True
+
     def get_ajax_output(self, changes):
 
         def get_form_factory(context, request):