diff --git a/lib/generators/active_record/devise_generator.rb b/lib/generators/active_record/devise_generator.rb
index 0382003fbd..9d2bd742f8 100644
--- a/lib/generators/active_record/devise_generator.rb
+++ b/lib/generators/active_record/devise_generator.rb
@@ -1,6 +1,7 @@
 require 'rails/generators/active_record'
 require 'generators/devise/orm_helpers'
 
+
 module ActiveRecord
   module Generators
     class DeviseGenerator < ActiveRecord::Generators::Base
@@ -9,14 +10,27 @@ class DeviseGenerator < ActiveRecord::Generators::Base
       include Devise::Generators::OrmHelpers
       source_root File.expand_path("../templates", __FILE__)
 
-      def generate_model
-        invoke "active_record:model", [name], :migration => false unless model_exists? && behavior == :invoke
-      end
-
       def copy_devise_migration
-        migration_template "migration.rb", "db/migrate/devise_create_#{table_name}"
+        exists = model_exists?
+        unless behavior == :revoke
+          unless exists
+            migration_template "migration.rb", "db/migrate/devise_create_#{table_name}"
+          else
+            migration_template "migration_existing.rb", "db/migrate/add_devise_to_#{table_name}"
+          end
+        else
+          if migration_exists?(table_name)
+            migration_template "migration_existing.rb", "db/migrate/add_devise_to_#{table_name}"
+          else
+            migration_template "migration.rb", "db/migrate/devise_create_#{table_name}"
+          end
+        end
       end
 
+      def generate_model
+        invoke "active_record:model", [name], :migration => false unless model_exists? && behavior == :invoke
+      end
+      
       def inject_devise_content
         inject_into_class(model_path, class_name, model_contents + <<CONTENT) if model_exists?
   # Setup accessible (or protected) attributes for your model
diff --git a/lib/generators/active_record/templates/migration_existing.rb b/lib/generators/active_record/templates/migration_existing.rb
new file mode 100644
index 0000000000..25477f6cf4
--- /dev/null
+++ b/lib/generators/active_record/templates/migration_existing.rb
@@ -0,0 +1,32 @@
+class AddDeviseTo<%= table_name.camelize %> < ActiveRecord::Migration
+  def self.up
+    change_table :<%= table_name %> do |t|
+      t.database_authenticatable :null => false
+      t.recoverable
+      t.rememberable
+      t.trackable
+    
+    # t.encryptable
+    # t.confirmable
+    # t.lockable :lock_strategy => :<%= Devise.lock_strategy %>, :unlock_strategy => :<%= Devise.unlock_strategy %>
+    # t.token_authenticatable
+
+<% for attribute in attributes -%>
+      t.<%= attribute.type %> :<%= attribute.name %>
+<% end -%>
+      #Uncomment below if timestamps were not included in your original model.
+      t.timestamps
+    end
+    add_index :<%= table_name %>, :email,                :unique => true
+    add_index :<%= table_name %>, :reset_password_token, :unique => true
+    # add_index :<%= table_name %>, :confirmation_token,   :unique => true
+    # add_index :<%= table_name %>, :unlock_token,         :unique => true
+    # add_index :<%= table_name %>, :authentication_token, :unique => true
+  end
+
+  def self.down
+    #By default, we don't want to make any assumption about how to roll back a migration when your
+    #model already existed. Please edit below which fields you would like to remove in this migration.
+    raise ActiveRecord::IrreversibleMigration   
+  end
+end
diff --git a/lib/generators/devise/orm_helpers.rb b/lib/generators/devise/orm_helpers.rb
index 99251f2868..644f83d11d 100644
--- a/lib/generators/devise/orm_helpers.rb
+++ b/lib/generators/devise/orm_helpers.rb
@@ -14,6 +14,14 @@ def model_contents
       def model_exists?
         File.exists?(File.join(destination_root, model_path))
       end
+      
+      def migration_exists?(table_name)
+        Dir.glob("#{File.join(destination_root, migration_path)}/[0-9]*_*.rb").grep(/\d+_add_devise_to_#{table_name}.rb$/).first
+      end
+      
+      def migration_path
+        @migration_path ||= File.join("db", "migrate")
+      end
 
       def model_path
         @model_path ||= File.join("app", "models", "#{file_path}.rb")
diff --git a/test/generators/active_record_generator_test.rb b/test/generators/active_record_generator_test.rb
index 8c33994c4d..f2b466ede4 100644
--- a/test/generators/active_record_generator_test.rb
+++ b/test/generators/active_record_generator_test.rb
@@ -13,9 +13,22 @@ class ActiveRecordGeneratorTest < Rails::Generators::TestCase
       assert_file "app/models/monster.rb", /devise/, /attr_accessible (:[a-z_]+(, )?)+/
       assert_migration "db/migrate/devise_create_monsters.rb"
     end
+    
+    test "update model migration when model exists" do
+      run_generator %w(monster)
+      assert_file "app/models/monster.rb"
+      run_generator %w(monster)
+      assert_migration "db/migrate/add_devise_to_monsters.rb"
+    end
   
     test "all files are properly deleted" do
       run_generator %w(monster)
+      run_generator %w(monster)
+      assert_migration "db/migrate/devise_create_monsters.rb"
+      assert_migration "db/migrate/add_devise_to_monsters.rb"
+      run_generator %w(monster), :behavior => :revoke
+      assert_no_migration "db/migrate/add_devise_to_monsters.rb"
+      assert_migration "db/migrate/devise_create_monsters.rb"
       run_generator %w(monster), :behavior => :revoke
       assert_no_file "app/models/monster.rb"
       assert_no_migration "db/migrate/devise_create_monsters.rb"