diff --git a/nested_projects/app/controllers/users_controller.rb b/nested_projects/app/controllers/users_controller.rb
index e2ab510fb..a37af0510 100644
--- a/nested_projects/app/controllers/users_controller.rb
+++ b/nested_projects/app/controllers/users_controller.rb
@@ -83,7 +83,7 @@ class UsersController < ApplicationController
     end
     @auth_sources = AuthSource.find(:all)
     @roles = Role.find_all_givable
-    @projects = Project.find(:all, :order => 'name', :conditions => "status=#{Project::STATUS_ACTIVE}") - @user.projects
+    @projects = Project.active.find(:all, :order => 'lft')
     @membership ||= Member.new
     @memberships = @user.memberships
   end
diff --git a/nested_projects/app/helpers/users_helper.rb b/nested_projects/app/helpers/users_helper.rb
index 18a80ef20..b9e990d6e 100644
--- a/nested_projects/app/helpers/users_helper.rb
+++ b/nested_projects/app/helpers/users_helper.rb
@@ -25,9 +25,11 @@ module UsersHelper
   end
   
   # Options for the new membership projects combo-box
-  def projects_options_for_select(projects)
+  def options_for_membership_project_select(user, projects)
     options = content_tag('option', "--- #{l(:actionview_instancetag_blank_option)} ---")
-    options << project_tree_options_for_select(projects)
+    options << project_tree_options_for_select(projects) do |p|
+      {:disabled => (user.projects.include?(p))}
+    end
     options
   end
   
diff --git a/nested_projects/app/views/users/_memberships.rhtml b/nested_projects/app/views/users/_memberships.rhtml
index 94b49159e..d1657fb98 100644
--- a/nested_projects/app/views/users/_memberships.rhtml
+++ b/nested_projects/app/views/users/_memberships.rhtml
@@ -31,7 +31,7 @@
 <p>
 <label><%=l(:label_project_new)%></label><br/>
 <% form_tag({ :action => 'edit_membership', :id => @user }) do %>
-<%= select_tag 'membership[project_id]', projects_options_for_select(@projects) %>
+<%= select_tag 'membership[project_id]', options_for_membership_project_select(@user, @projects) %>
 <%= l(:label_role) %>:
 <%= select_tag 'membership[role_id]', options_from_collection_for_select(@roles, "id", "name") %>
 <%= submit_tag l(:button_add) %>