diff --git a/core/modules/language/src/Form/NegotiationUrlForm.php b/core/modules/language/src/Form/NegotiationUrlForm.php
index f28a53d1a611f1e155335681401062fc5ba1f3df..eed7a38263b1b4c4d5e373467843deda36a4b989 100644
--- a/core/modules/language/src/Form/NegotiationUrlForm.php
+++ b/core/modules/language/src/Form/NegotiationUrlForm.php
@@ -59,7 +59,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#tree' => TRUE,
       '#title' => $this->t('Domain configuration'),
       '#open' => TRUE,
-      '#description' => $this->t('The domain names to use for these languages. Leave blank for the default language. Use with caution in a production environment.<strong>Modifying this value may break existing URLs. Use with caution in a production environment.</strong> Example: Specifying "de.example.com" as language domain for German will result in an URL like "http://de.example.com/contact".'),
+      '#description' => $this->t('The domain names to use for these languages. <strong>Modifying this value may break existing URLs. Use with caution in a production environment.</strong> Example: Specifying "de.example.com" as language domain for German will result in an URL like "http://de.example.com/contact".'),
       '#states' => array(
         'visible' => array(
           ':input[name="language_negotiation_url_part"]' => array(
@@ -130,10 +130,10 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
       $value = $form_state->getValue(array('domain', $langcode));
 
       if ($value === '') {
-        if (!$language->isDefault() && $form_state->getValue('language_negotiation_url_part') == LanguageNegotiationUrl::CONFIG_DOMAIN) {
+        if ($form_state->getValue('language_negotiation_url_part') == LanguageNegotiationUrl::CONFIG_DOMAIN) {
           // Throw a form error if the domain is blank for a non-default language,
           // although it is required for selected negotiation type.
-          $form_state->setErrorByName("domain][$langcode", $this->t('The domain may only be left blank for the default language.'));
+          $form_state->setErrorByName("domain][$langcode", $this->t('The domain may not be left blank for %language.', array('%language' => $language->name)));
         }
       }
       elseif (isset($count[$value]) && $count[$value] > 1) {
diff --git a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
index b1d40c0d4a4af9bf6e9744624d24c618108669fd..6a81438e8a15472bc9abda7481c2cdea7ae691d4 100644
--- a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
@@ -403,12 +403,23 @@ function testLanguageDomain() {
     );
     $this->drupalPostForm('admin/config/regional/language/detection', $edit, t('Save settings'));
 
+    // Do not allow blank domain.
+    $edit = array(
+      'language_negotiation_url_part' => LanguageNegotiationUrl::CONFIG_DOMAIN,
+      'domain[en]' => '',
+    );
+    $this->drupalPostForm('admin/config/regional/language/detection/url', $edit, t('Save configuration'));
+    $this->assertText('The domain may not be left blank for English', 'The form does not allow blank domains.');
+    $this->rebuildContainer();
+
     // Change the domain for the Italian language.
     $edit = array(
       'language_negotiation_url_part' => LanguageNegotiationUrl::CONFIG_DOMAIN,
+      'domain[en]' => gethostname(),
       'domain[it]' => 'it.example.com',
     );
     $this->drupalPostForm('admin/config/regional/language/detection/url', $edit, t('Save configuration'));
+    $this->assertText('The configuration options have been saved', 'Domain configuration is saved.');
     $this->rebuildContainer();
 
     // Build the link we're going to test.
diff --git a/core/modules/language/src/Tests/LanguageUrlRewritingTest.php b/core/modules/language/src/Tests/LanguageUrlRewritingTest.php
index ca3d93511ef06f7c70b0e09816dfa0662ff637e8..0d4c2cef0b65875c0744ba40c477fa2af007d069 100644
--- a/core/modules/language/src/Tests/LanguageUrlRewritingTest.php
+++ b/core/modules/language/src/Tests/LanguageUrlRewritingTest.php
@@ -101,6 +101,7 @@ function testDomainNameNegotiationPort() {
     $language_domain = 'example.fr';
     $edit = array(
       'language_negotiation_url_part' => LanguageNegotiationUrl::CONFIG_DOMAIN,
+      'domain[en]' => gethostname(),
       'domain[fr]' => $language_domain
     );
     $this->drupalPostForm('admin/config/regional/language/detection/url', $edit, t('Save configuration'));