diff --git a/core/lib/Drupal/Component/Utility/UrlHelper.php b/core/lib/Drupal/Component/Utility/UrlHelper.php
index 691413e..d0e67cb 100644
--- a/core/lib/Drupal/Component/Utility/UrlHelper.php
+++ b/core/lib/Drupal/Component/Utility/UrlHelper.php
@@ -366,4 +366,24 @@ public static function isValid($url, $absolute = FALSE) {
     }
   }
 
+  /**
+   * Returns the internal path from a uri of form user-path://internal/path.
+   *
+   * @param string $uri
+   *   The user entered URI
+   *
+   * @return string
+   *   The path part of the user-path URI.
+   *
+   * @throws \InvalidArgumentException
+   *   When the URI provided does not use the user-path:// scheme.
+   */
+  public static function userPathFromUri($uri) {
+    $parts = parse_url($uri);
+    if ($parts['scheme'] !== 'user-path') {
+      throw new \InvalidArgumentException(sprintf('Invalid user-path URI passed (%s), user-path URIs must use the user-path:// scheme', $parts['scheme']));
+    }
+    return ltrim($uri, 'user-path://');
+  }
+
 }
diff --git a/core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php b/core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
index a846a6e..8584d8d 100644
--- a/core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
+++ b/core/modules/link/src/Plugin/Field/FieldFormatter/LinkFormatter.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Utility\String;
 use Drupal\Component\Utility\Unicode;
+use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FormatterBase;
@@ -243,7 +244,7 @@ public function viewElements(FieldItemListInterface $items) {
   protected function buildUrl(LinkItemInterface $item) {
     $uri = $item->uri;
     if (parse_url($uri, PHP_URL_SCHEME) === 'user-path') {
-      $uri = substr($uri, 12);
+      $uri = UrlHelper::userPathFromUri($uri);
     }
 
     // @todo Consider updating the usage of the path validator with whatever
diff --git a/core/modules/link/src/Plugin/Field/FieldType/LinkItem.php b/core/modules/link/src/Plugin/Field/FieldType/LinkItem.php
index 8ab89fb..5f41270 100644
--- a/core/modules/link/src/Plugin/Field/FieldType/LinkItem.php
+++ b/core/modules/link/src/Plugin/Field/FieldType/LinkItem.php
@@ -8,6 +8,7 @@
 namespace Drupal\link\Plugin\Field\FieldType;
 
 use Drupal\Component\Utility\Random;
+use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemBase;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
@@ -154,7 +155,7 @@ public function isExternal() {
     // External links don't resolve to a route.
     $uri = $this->uri;
     if (parse_url($uri, PHP_URL_SCHEME) === 'user-path') {
-      $uri = substr($uri, 12);
+      $uri = UrlHelper::userPathFromUri($uri);
     }
     $url = \Drupal::pathValidator()->getUrlIfValid($uri);
     return $url->isExternal();
@@ -175,7 +176,7 @@ public static function mainPropertyName() {
   public function getUrl() {
     $uri = $this->uri;
     if (parse_url($uri, PHP_URL_SCHEME) === 'user-path') {
-      $uri = substr($uri, 12);
+      $uri = UrlHelper::userPathFromUri($uri);
     }
     return \Drupal::pathValidator()->getUrlIfValidWithoutAccessCheck($uri);
   }
diff --git a/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php b/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
index a055a3b..33d1a56 100644
--- a/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
+++ b/core/modules/link/src/Plugin/Field/FieldWidget/LinkWidget.php
@@ -8,6 +8,7 @@
 namespace Drupal\link\Plugin\Field\FieldWidget;
 
 use Drupal\Component\Utility\Unicode;
+use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\WidgetBase;
 use Drupal\Core\Form\FormStateInterface;
@@ -45,7 +46,7 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
     if (isset($items[$delta]->uri)) {
       $uri = $items[$delta]->uri;
       if (parse_url($uri, PHP_URL_SCHEME) === 'user-path') {
-        $uri = substr($uri, 12);
+        $uri = UrlHelper::userPathFromUri($uri);
       }
       if ($url = \Drupal::pathValidator()->getUrlIfValid($uri)) {
         $url->setOptions($items[$delta]->options ?: []);
diff --git a/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php b/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php
index d448add..f4d73b1 100644
--- a/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php
+++ b/core/modules/link/src/Plugin/Validation/Constraint/LinkTypeConstraint.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\link\Plugin\Validation\Constraint;
 
+use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\Url;
 use Drupal\link\LinkItemInterface;
 use Symfony\Component\Validator\Constraint;
@@ -56,7 +57,7 @@ public function validate($value, Constraint $constraint) {
       $url_string = $link_item->uri;
       $scheme = parse_url($url_string, PHP_URL_SCHEME);
       if ($scheme === 'user-path') {
-        $url_string = substr($url_string, 12);
+        $url_string = UrlHelper::userPathFromUri($url_string);
       }
       // Validate the url property.
       if (($scheme === 'user-path' || $scheme === 'base') && !($link_type & LinkItemInterface::LINK_INTERNAL)) {