diff --git a/src/collective/dms/basecontent/source.py b/src/collective/dms/basecontent/source.py
index ad0df17..8de8b44 100644
--- a/src/collective/dms/basecontent/source.py
+++ b/src/collective/dms/basecontent/source.py
@@ -8,6 +8,8 @@ class PrincipalSource(PrincipalSource):
 
     BLACKLIST = ('AuthenticatedUsers', 'Administrators', 'Site Administrators', 'Reviewers')
 
+    extra_default_values = None
+
     def search_principals(self, groups_first=False, **kw):
         if kw:
             results = self.acl_users.searchPrincipals(groups_first=True, **kw)
@@ -15,6 +17,10 @@ class PrincipalSource(PrincipalSource):
             # if no kw, we have been called from source __iter__ because
             # of Chosen widget populate_select attribute is set to True
             results = self.acl_users.searchGroups()
+            if self.extra_default_values:
+                # cf widget.py, CustomAjaxChosenMultiSelectionWidget::source
+                results = list(results)
+                results.extend(self.acl_users.searchUsers(id=self.extra_default_values))
         return [r for r in results if r.get('groupid', None) not in self.BLACKLIST]
 
     def searchGroups(self, **kwargs):
diff --git a/src/collective/dms/basecontent/widget.py b/src/collective/dms/basecontent/widget.py
index 1af492f..a226284 100644
--- a/src/collective/dms/basecontent/widget.py
+++ b/src/collective/dms/basecontent/widget.py
@@ -1,13 +1,34 @@
+import zope.component
+
+from zope.schema.interfaces import ISource, IContextSourceBinder
 from zope.interface import implementer
 import z3c.form.interfaces
 
+from z3c.form import interfaces, util, value
+
 from collective.z3cform.chosen.widget import AjaxChosenMultiSelectionWidget
 
+class CustomAjaxChosenMultiSelectionWidget(AjaxChosenMultiSelectionWidget):
+    @property
+    def source(self):
+        # We have a custom source property because we know it will be a
+        # PrincipalSource and it would only be prefilled with groups,
+        # while we may need to also have some users in that list if the
+        # default value has some. (otherwise to would be cleaned up as invalid
+        # values before presenting the form to the user, removing the users
+        # from the default value, only keeping the groups)
+        source = self.field.bind(self.context).value_type.source
+        adapter = zope.component.queryMultiAdapter(
+                (self.context, self.request, self.form, self.field, self),
+                interfaces.IValue, name='default')
+        if adapter:
+            source.extra_default_values = adapter.get()
+        return source
 
 @implementer(z3c.form.interfaces.IFieldWidget)
 def AjaxChosenMultiFieldWidget(field, request):
     widget = z3c.form.widget.FieldWidget(field,
-        AjaxChosenMultiSelectionWidget(request))
+        CustomAjaxChosenMultiSelectionWidget(request))
     widget.populate_select = True
     widget.ignoreMissing = True
     return widget