Index: .../zope.formlib/src/zope/formlib/form.py
===================================================================
--- .../zope.formlib/src/zope/formlib/form.py	(revision 82675)
+++ .../zope.formlib/src/zope/formlib/form.py	(working copy)
@@ -326,7 +326,12 @@
     if form_field.custom_widget is None:
         return component.getMultiAdapter((field, request), iface)
     else:
-        return form_field.custom_widget(field, request)
+        value_type = getattr(field, 'value_type', None)
+        if value_type:         
+            widget = form_field.custom_widget(field, value_type.vocabulary, request)
+        else:
+            widget = form_field.custom_widget(field, request)
+        return widget
 
 
 def getWidgetsData(widgets, form_prefix, data):