diff --git a/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php b/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
index 937491f..b9a4102 100644
--- a/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
+++ b/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
@@ -7,6 +7,7 @@
 use Drupal\Core\Field\WidgetBase;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\link\LinkItemInterface;
+use Drupal\link\Plugin\Field\FieldType\LinkItem;
 use Symfony\Component\Validator\ConstraintViolation;
 use Symfony\Component\Validator\ConstraintViolationListInterface;
 
@@ -133,13 +134,16 @@ public static function validateUriElement($element, FormStateInterface $form_sta
     $uri = static::getUserEnteredStringAsUri($element['#value']);
     $form_state->setValueForElement($element, $uri);
 
-    // If getUserEnteredStringAsUri() mapped the entered value to a 'internal:'
-    // URI , ensure the raw value begins with '/', '?' or '#'.
+    // If element is not LINK_EXTERNAL and getUserEnteredStringAsUri() mapped
+    // the entered value to a 'internal:' URI, ensure the raw value begins
+    // with '/', '?' or '#'.
     // @todo '<front>' is valid input for BC reasons, may be removed by
     //   https://www.drupal.org/node/2421941
-    if (parse_url($uri, PHP_URL_SCHEME) === 'internal' && !in_array($element['#value'][0], ['/', '?', '#'], TRUE) && substr($element['#value'], 0, 7) !== '<front>') {
-      $form_state->setError($element, t('Manually entered paths should start with /, ? or #.'));
-      return;
+    if ($element['#link_type'] !== LinkItem::LINK_EXTERNAL && parse_url($uri, PHP_URL_SCHEME) === 'internal') {
+      if (!in_array($element['#value'][0], ['/', '?', '#'], TRUE) && substr($element['#value'], 0, 7) !== '<front>') {
+        $form_state->setError($element, t('Manually entered paths should start with /, ? or #.'));
+        return;
+      }
     }
   }
 
diff --git a/core/modules/link/src/Tests/LinkFieldTest.php b/core/modules/link/src/Tests/LinkFieldTest.php
index 0b034d1..4eeaf56 100644
--- a/core/modules/link/src/Tests/LinkFieldTest.php
+++ b/core/modules/link/src/Tests/LinkFieldTest.php
@@ -163,6 +163,8 @@ public function testURLValidation() {
     // Test external URLs for 'link_type' = LinkItemInterface::LINK_EXTERNAL.
     $this->field->setSetting('link_type', LinkItemInterface::LINK_EXTERNAL);
     $this->field->save();
+    // Missing protocol schema.
+    $invalid_external_entries['www.drupal.org'] = $validation_error_1;
     $this->assertValidEntries($field_name, $valid_external_entries);
     $this->assertInvalidEntries($field_name, $valid_internal_entries + $invalid_external_entries);