diff --git a/app/models/nameserver.rb b/app/models/nameserver.rb
index 1880bd091..11537d3bc 100644
--- a/app/models/nameserver.rb
+++ b/app/models/nameserver.rb
@@ -5,7 +5,8 @@ class Nameserver < ActiveRecord::Base
   belongs_to :domain, required: true
 
   # rubocop: disable Metrics/LineLength
-  validates :hostname, presence: true, format: { with: /\A(([a-zA-Z0-9]|[a-zA-ZäöüõšžÄÖÜÕŠŽ0-9][a-zA-ZäöüõšžÄÖÜÕŠŽ0-9\-]*[a-zA-ZäöüõšžÄÖÜÕŠŽ0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])\z/ }
+  validates :hostname, presence: true#, format: { with: /\A(([a-zA-Z0-9]|[a-zA-ZäöüõšžÄÖÜÕŠŽ0-9][a-zA-ZäöüõšžÄÖÜÕŠŽ0-9\-]*[a-zA-ZäöüõšžÄÖÜÕŠŽ0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])\z/ }
+  validates :hostname, format: { with: /\A(([a-zA-Z0-9]|[a-zA-ZäöüõšžÄÖÜÕŠŽ0-9][a-zA-ZäöüõšžÄÖÜÕŠŽ0-9\-]*[a-zA-ZäöüõšžÄÖÜÕŠŽ0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])\z/ }, allow_blank: true
   validate :val_ipv4
   validate :val_ipv6
   validate :require_ip, if: :glue_record_required?
diff --git a/test/fixtures/nameservers.yml b/test/fixtures/nameservers.yml
index a03dc8cc9..8c3c021d6 100644
--- a/test/fixtures/nameservers.yml
+++ b/test/fixtures/nameservers.yml
@@ -1,4 +1,4 @@
-ns1:
+shop_ns1:
   hostname: ns1.bestnames.test
   ipv4:
     - 192.0.2.1
@@ -6,7 +6,7 @@ ns1:
     - 2001:db8::1
   domain: shop
 
-ns2:
+shop_ns2:
   hostname: ns2.bestnames.test
   ipv4:
     - 192.0.2.2
diff --git a/test/integration/api/nameservers/put_test.rb b/test/integration/api/nameservers/put_test.rb
index 034c885b7..416510541 100644
--- a/test/integration/api/nameservers/put_test.rb
+++ b/test/integration/api/nameservers/put_test.rb
@@ -1,24 +1,14 @@
 require 'test_helper'
 
 class APINameserversPutTest < ActionDispatch::IntegrationTest
-  def setup
-    @registrar = registrars(:bestnames)
-  end
-
-  def test_deletes_old_nameservers
-    previous_nameserver_ids = @registrar.nameservers.where(hostname: 'ns1.bestnames.test').ids
-    request_params = { format: :json, data: { type: 'nameserver', id: 'ns1.bestnames.test',
-                                              attributes: { hostname: 'ns55.bestnames.test' } } }
-
-    put '/repp/v1/registrar/nameservers', request_params, { 'HTTP_AUTHORIZATION' => http_auth_key }
-    refute @registrar.nameservers(true).where(id: previous_nameserver_ids).exists?
-  end
-
-  def test_creates_new_nameservers
+  def test_replaces_registrar_nameservers
+    old_nameserver_ids = [nameservers(:shop_ns1).id,
+                          nameservers(:airport_ns1).id,
+                          nameservers(:metro_ns1).id]
     request_params = { format: :json, data: { type: 'nameserver', id: 'ns1.bestnames.test',
                                               attributes: { hostname: 'ns55.bestnames.test' } } }
     put '/repp/v1/registrar/nameservers', request_params, { 'HTTP_AUTHORIZATION' => http_auth_key }
-    assert_equal 2, @registrar.nameservers.where(hostname: 'ns55.bestnames.test').size
+    assert_empty (old_nameserver_ids & registrars(:bestnames).nameservers(true).ids)
   end
 
   def test_saves_all_attributes
@@ -33,14 +23,22 @@ class APINameserversPutTest < ActionDispatch::IntegrationTest
     assert_equal ['2001:DB8::55'], new_nameserver.ipv6
   end
 
+  def test_keeps_other_nameserver_intact
+    request_params = { format: :json, data: { type: 'nameserver', id: 'ns1.bestnames.test',
+                                              attributes: { hostname: 'ns55.bestnames.test' } } }
+
+    other_nameserver_hash = nameservers(:shop_ns2).attributes
+    put '/repp/v1/registrar/nameservers', request_params, { 'HTTP_AUTHORIZATION' => http_auth_key }
+    assert_equal other_nameserver_hash, nameservers(:shop_ns2).reload.attributes
+  end
+
   def test_keeps_other_registrar_nameservers_intact
     request_params = { format: :json, data: { type: 'nameserver', id: 'ns1.bestnames.test',
                                               attributes: { hostname: 'ns55.bestnames.test' } } }
 
-    other_registrar_nameserver_ids = registrars(:goodnames).nameservers.ids
-    assert other_registrar_nameserver_ids.any?
+    nameserver_hash = nameservers(:metro_ns1).attributes
     put '/repp/v1/registrar/nameservers', request_params, { 'HTTP_AUTHORIZATION' => http_auth_key }
-    assert_equal other_registrar_nameserver_ids, registrars(:goodnames).nameservers(true).ids
+    assert_equal nameserver_hash, nameservers(:metro_ns1).reload.attributes
   end
 
   def test_returns_new_nameserver_record
diff --git a/test/models/nameserver/glue_record_test.rb b/test/models/nameserver/glue_record_test.rb
index 4a7f55b0c..7d5e39d8d 100644
--- a/test/models/nameserver/glue_record_test.rb
+++ b/test/models/nameserver/glue_record_test.rb
@@ -2,7 +2,7 @@ require 'test_helper'
 
 class NameserverGlueRecordTest < ActiveSupport::TestCase
   def setup
-    @nameserver = nameservers(:ns1)
+    @nameserver = nameservers(:shop_ns1)
   end
 
   def test_invalid_without_ip_if_glue_record_is_required
diff --git a/test/models/nameserver_test.rb b/test/models/nameserver_test.rb
index 377ff446a..45c1d0fb2 100644
--- a/test/models/nameserver_test.rb
+++ b/test/models/nameserver_test.rb
@@ -2,7 +2,7 @@ require 'test_helper'
 
 class NameserverTest < ActiveSupport::TestCase
   def setup
-    @nameserver = nameservers(:ns1)
+    @nameserver = nameservers(:shop_ns1)
   end
 
   def test_valid
@@ -19,8 +19,22 @@ class NameserverTest < ActiveSupport::TestCase
     assert @nameserver.invalid?
   end
 
+  def test_hostname_format_validation
+    @nameserver.hostname = 'foo_bar'
+    assert @nameserver.invalid?
+
+    @nameserver.hostname = 'foo.bar'
+    assert @nameserver.valid?
+
+    @nameserver.hostname = 'äöüõšž.ÄÖÜÕŠŽ.umlauts'
+    assert @nameserver.valid?
+  end
+
   def test_hostnames
-    assert_equal %w[ns1.bestnames.test ns2.bestnames.test], Nameserver.hostnames
+    assert_equal %w[ns1.bestnames.test
+      ns2.bestnames.test
+      ns1.bestnames.test
+      ns1.bestnames.test], Nameserver.hostnames
   end
 
   def test_normalizes_hostname