diff --git a/lib/costs_issue_observer.rb b/lib/costs_issue_observer.rb
index 656abdd6d0..4ae08bbed4 100644
--- a/lib/costs_issue_observer.rb
+++ b/lib/costs_issue_observer.rb
@@ -6,5 +6,12 @@ class CostsIssueObserver < ActiveRecord::Observer
       CostEntry.update_all({:project_id => issue.project_id}, {:issue_id => id})
     end 
   end
+  
+  def before_update(issue)
+    # FIXME: remove this method once controller_issues_move_before_save is in 0.9-stable
+    if issue.project_id_changed? && issue.cost_object_id && !issue.project.cost_object_ids.include?(issue.cost_object_id)
+      issue.cost_object = nil
+    end
+  end
 end
     
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