diff --git a/app/controllers/todos_controller.rb b/app/controllers/todos_controller.rb
index 26aabab2..dfa0f992 100644
--- a/app/controllers/todos_controller.rb
+++ b/app/controllers/todos_controller.rb
@@ -145,7 +145,7 @@ class TodosController < ApplicationController
     @todo = Todo.find(params['successor'])
     @original_state = @todo.state
     # Add predecessor
-    @todo.predecessors << @predecessor
+    @todo.add_predecessor(@predecessor)
     @todo.state = 'pending'
     @saved = @todo.save
     respond_to do |format|
diff --git a/app/models/todo.rb b/app/models/todo.rb
index 621cd1b6..6d5217e0 100644
--- a/app/models/todo.rb
+++ b/app/models/todo.rb
@@ -80,13 +80,15 @@ class Todo < ActiveRecord::Base
     if !show_from.blank? && show_from < user.date
       errors.add("show_from", "must be a date in the future")
     end
-    # Validate predecessors array
-    @predecessor_array.each do |description|
-      t = Todo.find_by_description(description)
-      if t.nil?
-        errors.add("Depends on:", "Could not find action '#{description}'")
-      else
-        errors.add("Depends on:", "Adding '#{description}' would create a circular dependency") if is_successor?(t)
+    unless @predecessor_array.nil?
+      # Validate predecessors array    
+      @predecessor_array.each do |description|
+        t = Todo.find_by_description(description)
+        if t.nil?
+          errors.add("Depends on:", "Could not find action '#{description}'")
+        else
+          errors.add("Depends on:", "Adding '#{description}' would create a circular dependency") if is_successor?(t)
+        end
       end
     end
   end
@@ -225,6 +227,11 @@ class Todo < ActiveRecord::Base
     end
   end
   
+  def add_predecessor(t)
+    @predecessor_array = predecessors.map(&:description)
+    @predecessor_array << t.description
+  end
+  
   # Rich Todo API
   
   def self.from_rich_message(user, default_context_id, description, notes)