diff --git a/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php b/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
index 97015d5bef..2126d8e601 100644
--- a/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
+++ b/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
@@ -143,13 +143,34 @@ 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 an '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) && !str_starts_with($element['#value'], '<front>')) {
-      $form_state->setError($element, new TranslatableMarkup('Manually entered paths should start with one of the following characters: / ? #'));
-      return;
+    // Check if it is an internal link or an external link missing protocol.
+    if (parse_url($uri, PHP_URL_SCHEME) === 'internal') {
+
+      // Ensure internal links raw value begins with with '/', '?' or '#'.
+      if (!in_array($element['#value'][0], ['/', '?', '#'], TRUE)) {
+
+        // @todo '<front>' is valid input for BC reasons, may be removed by
+        //   https://www.drupal.org/node/2421941
+        if (substr($element['#value'], 0, 7) !== '<front>') {
+
+          // Displays an error message according to the link type.
+          switch ($element['#link_type']) {
+            case LinkItemInterface::LINK_EXTERNAL:
+              $error_message = 'External links must be a full URL and include its protocol, such as %link_example.';
+              break;
+
+            case LinkItemInterface::LINK_INTERNAL:
+              $error_message = 'Use a title of a piece of content to select it, or enter an internal path starting with /, ? or #.';
+              break;
+
+            // Error message for LinkItemInterface::LINK_GENERIC.
+            default:
+              $error_message = 'Use a title of a piece of content to select it, or enter an internal path starting with /, ? or #. External links must be a full URL and include its protocol, such as %link_example.';
+          }
+          $form_state->setError($element, t($error_message, ['%link_example' => 'http://example.com']));
+          return;
+        }
+      }
     }
   }