diff --git a/app/models/ns.rb b/app/models/ns.rb
index f12b135..dab46bd 100644
--- a/app/models/ns.rb
+++ b/app/models/ns.rb
@@ -1,6 +1,6 @@
 class NS < Record
-  validates :content, presence: true, hostname: true
+  validates :content, presence: true, hostname: true, not_ip: true
 
   before_validation :remove_terminating_dot
 end
 
diff --git a/lib/not_ip_validator.rb b/lib/not_ip_validator.rb
new file mode 100644
index 0000000..bea8b89
--- /dev/null
+++ b/lib/not_ip_validator.rb
@@ -0,0 +1,8 @@
+class NotIpValidator < ActiveModel::EachValidator
+  # Add an Atribute error if this a valid IP address.
+  def validate_each(record, attribute, value)
+    if [Ipv4Validator, Ipv6Validator].any? { |fam| fam.valid?(value) }
+      record.errors[attribute] << 'should not be an IP address'
+    end
+  end
+end
diff --git a/test/models/ns_test.rb b/test/models/ns_test.rb
index c0400bc..f6d861c 100644
--- a/test/models/ns_test.rb
+++ b/test/models/ns_test.rb
@@ -1,193 +1,207 @@
 require 'test_helper'
 
 class NSTest < ActiveSupport::TestCase
   setup do
     @record = build(:ns)
   end
 
   test 'save' do
     @record.save
 
     assert_empty @record.errors
   end
 
+  test 'doesnt allow IPv4 address as content' do
+    @record.content = '1.2.3.4'
+    @record.save
+
+    assert_not_empty @record.errors[:content]
+  end
+
+  test 'doesnt allow IPv6 address as content' do
+    @record.content = '::1'
+    @record.save
+
+    assert_not_empty @record.errors[:content]
+  end
+
   test 'chop terminating dot' do
     @record.content = 'with-dot.example.com.'
     @record.save!
     @record.reload
 
     assert_equal 'with-dot.example.com', @record.content
   end
 
   test 'drop privileges on zone NS records' do
     @record.drop_privileges = true
     @record.save
 
     assert_not_empty @record.errors[:name]
   end
 
   test 'doesnt drop privileges on non zone NS records' do
     @record.name = 'other'
     @record.drop_privileges = true
 
     @record.save
 
     assert_empty @record.errors[:name]
   end
 
   class ClasslessDelegation < ActiveSupport::TestCase
     setup do
       @record = build(:cd_ns, name: '192/29')
       @domain = @record.domain
     end
 
     test 'creates delegation' do
       assert @record.save
       assert @record.classless_delegation?
 
       octets = [192, 193, 194, 195, 196, 197, 198, 199]
 
       assert_equal octets.size, @domain.records.where(type: 'CNAME').count
 
       octets.each { |octet|
         cname = @domain.records.where(type: 'CNAME', name: "#{octet}.#{@domain.name}").first
 
         assert cname, "#{octet} delegation"
         assert_not cname.editable?, "#{octet} editable"
         assert cname.classless_delegated?, "#{octet} classless_delegated"
       }
     end
 
     test 'delete delegation' do
       assert @record.save
 
       @record.destroy
       assert_equal 0, @domain.records.where(type: 'CNAME').count, 'zero delegations'
     end
 
     [
       '0/24', # too big
       '0/32', # too small
       '191/29',
       '-192/29',
       '192/-29',
       '192/29/29',
       '192',
     ].each { |del|
       test "invalid delegation #{del}" do
         @record.name = del
         @record.save!
         assert_not @record.classless_delegation?
 
         assert_equal 0, @domain.records.where(type: 'CNAME').count, "0 CNAMEs for #{del}"
       end
     }
 
     test 'add errors when a record already exists' do
       create(:v4_ptr, domain: @domain, name: '194')
 
       assert_not @record.save, 'delegation with records should fail'
       assert_not_empty @record.errors[:name]
     end
 
     test 'allow second delegation with a different NS' do
       @record.save!
 
       assert_no_difference "@domain.records.where(type: 'CNAME').count" do
         NS.create!(domain: @domain, name: @record.name, content: 'ns-other.example.com')
       end
     end
 
     test 'drop records after all NS are deleted' do
       @record.save!
       second = NS.create!(domain: @domain, name: @record.name, content: 'ns-other.example.com')
 
       # CNAMEs are not deleted
       assert_no_difference '@domain.records.where(type: "CNAME").count' do
         second.destroy
       end
 
       # Deleting the last NS delegation should delete all CNAMEs
       @record.destroy
       assert_equal 0, @domain.records.where(type: 'CNAME').count, 'zero delegations'
     end
   end
 
   class ClasslessDelegationWithDash < ActiveSupport::TestCase
     setup do
       @record = build(:cd_ns, name: '192-29')
       @domain = @record.domain
     end
 
     test 'creates delegation' do
       assert @record.save
       assert @record.classless_delegation?
 
       octets = [192, 193, 194, 195, 196, 197, 198, 199]
 
       assert_equal octets.size, @domain.records.where(type: 'CNAME').count
 
       octets.each { |octet|
         cname = @domain.records.where(type: 'CNAME', name: "#{octet}.#{@domain.name}").first
 
         assert cname, "#{octet} delegation"
         assert_not cname.editable?, "#{octet} editable"
         assert cname.classless_delegated?, "#{octet} classless_delegated"
       }
     end
 
     test 'delete delegation' do
       assert @record.save
 
       @record.destroy
       assert_equal 0, @domain.records.where(type: 'CNAME').count, 'zero delegations'
     end
 
     [
       '0-24', # too big
       '0-32', # too small
       '191-29',
       '-192-29',
       '192--29',
       '192-29-29',
       '192',
     ].each { |del|
       test "invalid delegation #{del}" do
         @record.name = del
         @record.save!
         assert_not @record.classless_delegation?
 
         assert_equal 0, @domain.records.where(type: 'CNAME').count, "0 CNAMEs for #{del}"
       end
     }
 
     test 'add errors when a record already exists' do
       create(:v4_ptr, domain: @domain, name: '194')
 
       assert_not @record.save, 'delegation with records should fail'
       assert_not_empty @record.errors[:name]
     end
 
     test 'allow second delegation with a different NS' do
       @record.save!
 
       assert_no_difference "@domain.records.where(type: 'CNAME').count" do
         NS.create!(domain: @domain, name: @record.name, content: 'ns-other.example.com')
       end
     end
 
     test 'drop records after all NS are deleted' do
       @record.save!
       second = NS.create!(domain: @domain, name: @record.name, content: 'ns-other.example.com')
 
       # CNAMEs are not deleted
       assert_no_difference '@domain.records.where(type: "CNAME").count' do
         second.destroy
       end
 
       # Deleting the last NS delegation should delete all CNAMEs
       @record.destroy
       assert_equal 0, @domain.records.where(type: 'CNAME').count, 'zero delegations'
     end
   end
 end