diff --git a/Gemfile b/Gemfile
index d2ef306..3336044 100644
--- a/Gemfile
+++ b/Gemfile
@@ -73,6 +73,7 @@ group :test, :development do
   gem 'rspec-rails', '~> 3.1.0'
   gem 'rspec-its', '~> 1.1.0'
   gem 'rspec-collection_matchers', '~> 1.1.2'
+  gem 'rspec-mocks', '~> 3.1.3'
 end
 
 group :test do
diff --git a/Gemfile.lock b/Gemfile.lock
index 700a33e..786c029 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -365,6 +365,7 @@ DEPENDENCIES
   rails_config (~> 0.4.2)
   rspec-collection_matchers (~> 1.1.2)
   rspec-its (~> 1.1.0)
+  rspec-mocks (~> 3.1.3)
   rspec-rails (~> 3.1.0)
   sass-rails (~> 4.0.4)
   seedbank (~> 0.3.0)
diff --git a/app/models/domain/tree_structure.rb b/app/models/domain/tree_structure.rb
index ba4ba08..533c87d 100644
--- a/app/models/domain/tree_structure.rb
+++ b/app/models/domain/tree_structure.rb
@@ -12,7 +12,7 @@ class Domain < ActiveRecord::Base
   after_save :sync_children
   
   # this goes after sync_parent, to order callbacks correctly 
-  acts_as_nested_interval virtual_root: true, dependent: :nullify
+  acts_as_nested_interval virtual_root: true, dependent: :restrict_with_error
   
   validate :domain_ownership
   def domain_ownership
diff --git a/spec/models/domain_spec.rb b/spec/models/domain_spec.rb
index dde52a6..1437d8a 100644
--- a/spec/models/domain_spec.rb
+++ b/spec/models/domain_spec.rb
@@ -67,7 +67,7 @@ describe Domain do
 
     User.do_as(user) do
       # stub a parent domain on another user account, with no permissions present
-      mock_domain = mock(
+      mock_domain = double(
         :user_id => user3.id, 
         :user => user3, 
         :name => 'x',