diff --git a/core/modules/datetime_range/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php b/core/modules/datetime_range/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php
index 7ac4330..f5ebb8c 100644
--- a/core/modules/datetime_range/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php
+++ b/core/modules/datetime_range/src/Plugin/Field/FieldFormatter/DateRangeDefaultFormatter.php
@@ -57,7 +57,7 @@ public function viewElements(FieldItemListInterface $items, $langcode) {
           ];
         }
         else {
-          $elements[$delta] = $this->buildDate($start_date);
+          $elements[$delta] = $this->buildDateWithIsoAttribute($start_date);
         }
 
         if (!empty($item->_attributes)) {
diff --git a/core/modules/datetime_range/src/Tests/DateRangeFieldTest.php b/core/modules/datetime_range/src/Tests/DateRangeFieldTest.php
index 11c3c52..078a67e 100644
--- a/core/modules/datetime_range/src/Tests/DateRangeFieldTest.php
+++ b/core/modules/datetime_range/src/Tests/DateRangeFieldTest.php
@@ -258,6 +258,69 @@ public function testDateRangeField() {
       $expected = $start_date->format($this->displayOptions['settings']['date_format']) . ' - ' . $end_date->format($this->displayOptions['settings']['date_format']);
       $this->renderTestEntity($id);
       $this->assertText($expected, new FormattableMarkup('Formatted date field using daterange_custom format displayed as %expected.', array('%expected' => $expected)));
+
+      // Test formatters when start date and end date are the same
+      $this->drupalGet('entity_test/add');
+      $value = '2012-12-31 00:00:00';
+      $start_date = new DrupalDateTime($value, 'UTC');
+
+      $date_format = DateFormat::load('html_date')->getPattern();
+      $time_format = DateFormat::load('html_time')->getPattern();
+
+      $edit = array(
+        "{$field_name}[0][value][date]" => $start_date->format($date_format),
+        "{$field_name}[0][end_value][date]" => $start_date->format($date_format),
+      );
+
+      $this->drupalPostForm(NULL, $edit, t('Save'));
+      preg_match('|entity_test/manage/(\d+)|', $this->url, $match);
+      $id = $match[1];
+      $this->assertText(t('entity_test @id has been created.', array('@id' => $id)));
+
+      datetime_date_default_time($start_date);
+
+      $this->displayOptions = [
+        'type' => 'daterange_default',
+        'label' => 'hidden',
+        'settings' => [
+            'format_type' => 'long',
+            'separator' => 'THESEPARATOR',
+          ] + $this->defaultSettings,
+      ];
+
+      entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+        ->setComponent($field_name, $this->displayOptions)
+        ->save();
+
+      $start_expected = $this->dateFormatter->format($start_date->getTimestamp(), 'long', '', DATETIME_STORAGE_TIMEZONE);
+      $start_expected_iso = $this->dateFormatter->format($start_date->getTimestamp(), 'custom', 'Y-m-d\TH:i:s\Z', DATETIME_STORAGE_TIMEZONE);
+      $this->renderTestEntity($id);
+      $this->assertFieldByXPath('//time[@datetime="' . $start_expected_iso . '"]', $start_expected, new FormattableMarkup('Formatted date field using %value format displayed as %expected with %expected_iso attribute.', [
+        '%value' => 'long',
+        '%expected' => $start_expected,
+        '%expected_iso' => $start_expected_iso,
+      ]));
+      $this->assertNoText(' THESEPARATOR ', 'Separator not found on page');
+
+      $this->displayOptions['type'] = 'daterange_plain';
+      $this->displayOptions['settings'] = $this->defaultSettings;
+      entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+        ->setComponent($field_name, $this->displayOptions)
+        ->save();
+      $expected = $start_date->format(DATETIME_DATE_STORAGE_FORMAT);
+      $this->renderTestEntity($id);
+      $this->assertText($expected, new FormattableMarkup('Formatted date field using plain format displayed as %expected.', array('%expected' => $expected)));
+      $this->assertNoText(' THESEPARATOR ', 'Separator not found on page');
+
+      $this->displayOptions['type'] = 'daterange_custom';
+      $this->displayOptions['settings'] = array('date_format' => 'm/d/Y') + $this->defaultSettings;
+      entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+        ->setComponent($field_name, $this->displayOptions)
+        ->save();
+      $expected = $start_date->format($this->displayOptions['settings']['date_format']);
+      $this->renderTestEntity($id);
+      $this->assertText($expected, new FormattableMarkup('Formatted date field using daterange_custom format displayed as %expected.', array('%expected' => $expected)));
+      $this->assertNoText(' THESEPARATOR ', 'Separator not found on page');
     }
   }
 
@@ -355,6 +418,66 @@ public function testDatetimeRangeField() {
     $expected .= ' - ' . $end_date->format($this->displayOptions['settings']['date_format'], ['timezone' => 'America/New_York']);
     $this->renderTestEntity($id);
     $this->assertText($expected, new FormattableMarkup('Formatted date field using daterange_custom format displayed as %expected.', array('%expected' => $expected)));
+
+    // Test formatters when start date and end date are the same
+    $this->drupalGet('entity_test/add');
+    $value = '2012-12-31 00:00:00';
+    $start_date = new DrupalDateTime($value, 'UTC');
+    $start_date->setTimezone(timezone_open(drupal_get_user_timezone()));
+
+    $date_format = DateFormat::load('html_date')->getPattern();
+    $time_format = DateFormat::load('html_time')->getPattern();
+
+    $edit = array(
+      "{$field_name}[0][value][date]" => $start_date->format($date_format),
+      "{$field_name}[0][value][time]" => $start_date->format($time_format),
+      "{$field_name}[0][end_value][date]" => $start_date->format($date_format),
+      "{$field_name}[0][end_value][time]" => $start_date->format($time_format),
+    );
+
+    $this->drupalPostForm(NULL, $edit, t('Save'));
+    preg_match('|entity_test/manage/(\d+)|', $this->url, $match);
+    $id = $match[1];
+    $this->assertText(t('entity_test @id has been created.', array('@id' => $id)));
+
+    $this->displayOptions = [
+      'type' => 'daterange_default',
+      'label' => 'hidden',
+      'settings' => [
+        'format_type' => 'long',
+        'separator' => 'THESEPARATOR',
+      ] + $this->defaultSettings,
+    ];
+
+    entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+      ->setComponent($field_name, $this->displayOptions)
+      ->save();
+
+    $start_expected = $this->dateFormatter->format($start_date->getTimestamp(), 'long');
+    $start_expected_iso = $this->dateFormatter->format($start_date->getTimestamp(), 'custom', 'Y-m-d\TH:i:s\Z', 'UTC');
+    $this->renderTestEntity($id);
+    $this->assertFieldByXPath('//time[@datetime="' . $start_expected_iso . '"]', $start_expected, new FormattableMarkup('Formatted date field using %value format displayed as %expected with %expected_iso attribute.', ['%value' => 'long', '%expected' => $start_expected, '%expected_iso' => $start_expected_iso]));
+    $this->assertNoText(' THESEPARATOR ', 'Separator not found on page');
+
+    $this->displayOptions['type'] = 'daterange_plain';
+    $this->displayOptions['settings'] = $this->defaultSettings;
+    entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+      ->setComponent($field_name, $this->displayOptions)
+      ->save();
+    $expected = $start_date->format(DATETIME_DATETIME_STORAGE_FORMAT);
+    $this->renderTestEntity($id);
+    $this->assertText($expected, new FormattableMarkup('Formatted date field using plain format displayed as %expected.', array('%expected' => $expected)));
+    $this->assertNoText(' THESEPARATOR ', 'Separator not found on page');
+
+    $this->displayOptions['type'] = 'daterange_custom';
+    $this->displayOptions['settings'] = ['date_format' => 'm/d/Y g:i:s A'] + $this->defaultSettings;
+    entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+      ->setComponent($field_name, $this->displayOptions)
+      ->save();
+    $expected = $start_date->format($this->displayOptions['settings']['date_format']);
+    $this->renderTestEntity($id);
+    $this->assertText($expected, new FormattableMarkup('Formatted date field using daterange_custom format displayed as %expected.', array('%expected' => $expected)));
+    $this->assertNoText(' THESEPARATOR ', 'Separator not found on page');
   }
 
   /**
@@ -446,6 +569,68 @@ public function testAlldayRangeField() {
     $expected .= ' - ' . $end_date->format($this->displayOptions['settings']['date_format'], ['timezone' => 'America/New_York']);
     $this->renderTestEntity($id);
     $this->assertText($expected, new FormattableMarkup('Formatted date field using daterange_custom format displayed as %expected.', array('%expected' => $expected)));
+
+    // Test formatters when start date and end date are the same
+    $this->drupalGet('entity_test/add');
+
+    $value = '2012-12-31 00:00:00';
+    $start_date = new DrupalDateTime($value, timezone_open(drupal_get_user_timezone()));
+    $end_value = '2012-12-31 23:59:59';
+    $end_date = new DrupalDateTime($end_value, timezone_open(drupal_get_user_timezone()));
+
+    $date_format = DateFormat::load('html_date')->getPattern();
+    $time_format = DateFormat::load('html_time')->getPattern();
+
+    $edit = array(
+      "{$field_name}[0][value][date]" => $start_date->format($date_format),
+      "{$field_name}[0][end_value][date]" => $start_date->format($date_format),
+    );
+    $this->drupalPostForm(NULL, $edit, t('Save'));
+    preg_match('|entity_test/manage/(\d+)|', $this->url, $match);
+    $id = $match[1];
+    $this->assertText(t('entity_test @id has been created.', array('@id' => $id)));
+
+    $this->displayOptions = [
+      'type' => 'daterange_default',
+      'label' => 'hidden',
+      'settings' => [
+        'format_type' => 'long',
+        'separator' => 'THESEPARATOR',
+      ] + $this->defaultSettings,
+    ];
+
+    entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+      ->setComponent($field_name, $this->displayOptions)
+      ->save();
+
+    $start_expected = $this->dateFormatter->format($start_date->getTimestamp(), 'long');
+    $start_expected_iso = $this->dateFormatter->format($start_date->getTimestamp(), 'custom', 'Y-m-d\TH:i:s\Z', 'UTC');
+    $end_expected = $this->dateFormatter->format($end_date->getTimestamp(), 'long');
+    $end_expected_iso = $this->dateFormatter->format($end_date->getTimestamp(), 'custom', 'Y-m-d\TH:i:s\Z', 'UTC');
+    $this->renderTestEntity($id);
+    $this->assertFieldByXPath('//time[@datetime="' . $start_expected_iso . '"]', $start_expected, new FormattableMarkup('Formatted date field using %value format displayed as %expected with %expected_iso attribute.', ['%value' => 'long', '%expected' => $start_expected, '%expected_iso' => $start_expected_iso]));
+    $this->assertFieldByXPath('//time[@datetime="' . $end_expected_iso . '"]', $end_expected, new FormattableMarkup('Formatted date field using %value format displayed as %expected with %expected_iso attribute.', ['%value' => 'long', '%expected' => $end_expected, '%expected_iso' => $end_expected_iso]));
+    $this->assertText(' THESEPARATOR ', 'Found proper separator');
+
+    $this->displayOptions['type'] = 'daterange_plain';
+    entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+      ->setComponent($field_name, $this->displayOptions)
+      ->save();
+    $expected = $start_date->format(DATETIME_DATETIME_STORAGE_FORMAT) . ' THESEPARATOR ' . $end_date->format(DATETIME_DATETIME_STORAGE_FORMAT);
+    $this->renderTestEntity($id);
+    $this->assertText($expected, new FormattableMarkup('Formatted date field using plain format displayed as %expected.', array('%expected' => $expected)));
+    $this->assertText(' THESEPARATOR ', 'Found proper separator');
+
+    $this->displayOptions['type'] = 'daterange_custom';
+    $this->displayOptions['settings']['date_format'] = 'm/d/Y';
+    entity_get_display($this->field->getTargetEntityTypeId(), $this->field->getTargetBundle(), 'full')
+      ->setComponent($field_name, $this->displayOptions)
+      ->save();
+    $expected = $start_date->format($this->displayOptions['settings']['date_format']) . ' THESEPARATOR ' . $end_date->format($this->displayOptions['settings']['date_format']);
+    $this->renderTestEntity($id);
+    $this->assertText($expected, new FormattableMarkup('Formatted date field using daterange_custom format displayed as %expected.', array('%expected' => $expected)));
+    $this->assertText(' THESEPARATOR ', 'Found proper separator');
+
   }
 
   /**
@@ -974,7 +1159,6 @@ public function testInvalidField() {
     $this->fieldStorage->save();
     $field_name = $this->fieldStorage->getName();
 
-    // Display creation form.
     $this->drupalGet('entity_test/add');
     $this->assertFieldByName("{$field_name}[0][value][date]", '', 'Start date element found.');
     $this->assertFieldByName("{$field_name}[0][value][time]", '', 'Start time element found.');