diff --git a/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php b/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php
index 78cebbe..9d9df04 100644
--- a/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php
+++ b/core/modules/rest/src/Plugin/rest/resource/UserRegistrationResource.php
@@ -97,6 +97,37 @@ public static function create(ContainerInterface $container, array $configuratio
    * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
    */
   public function post(UserInterface $account = NULL) {
+    $this->ensureAccountCanRegister($account);
+
+    // Only active new users if visitors are allowed to register and no email
+    // verification required.
+    if ($this->userSettings->get('register') == USER_REGISTER_VISITORS && !$this->userSettings->get('verify_mail')) {
+      $account->activate();
+    }
+    else {
+      $account->block();
+    }
+
+    $this->checkEditFieldAccess($account);
+
+    // Make sure that the user entity is valid (email and name are valid).
+    $this->validate($account);
+
+    // Create the account.
+    $account->save();
+
+    $this->sendEmailNotifications($account);
+
+    return new ModifiedResourceResponse($account, 200);
+  }
+
+  /**
+   * Ensure the account can be registered in this request.
+   *
+   * @param \Drupal\user\UserInterface $account
+   *   The user account to register.
+   */
+  protected function ensureAccountCanRegister(UserInterface $account = NULL) {
     if ($account === NULL) {
       throw new BadRequestHttpException('No user account data for registration received.');
     }
@@ -113,42 +144,32 @@ public function post(UserInterface $account = NULL) {
     if (!$this->currentUser->isAnonymous()) {
       throw new AccessDeniedHttpException('Only anonymous users can register users.');
     }
-    $approvalSettings = $this->userSettings->get('register');
 
     // Verify that the current user can register a user account.
-    if ($approvalSettings == USER_REGISTER_ADMINISTRATORS_ONLY) {
+    if ($this->userSettings->get('register') == USER_REGISTER_ADMINISTRATORS_ONLY) {
       throw new AccessDeniedHttpException('You cannot register a new user account.');
     }
-    // Only active new users if visitors are allowed to register and no email
-    // verification required.
-    if ($approvalSettings == USER_REGISTER_VISITORS && !$this->userSettings->get('verify_mail')) {
-      $account->activate();
-    }
-    else {
-      $account->block();
-    }
-
-    $this->checkEditFieldAccess($account);
-
-    // Make sure that the user entity is valid (email and name are valid).
-    $this->validate($account);
-
-    // Create the account.
-    $account->save();
+  }
 
+  /**
+   * Sends email notifications if necessary for user that was registered.
+   *
+   * @param \Drupal\user\UserInterface $account
+   *   The user account.
+   */
+  protected function sendEmailNotifications(UserInterface $account) {
+    $approval_settings = $this->userSettings->get('register');
     // No e-mail verification is required. Activating the user.
-    if ($approvalSettings == USER_REGISTER_VISITORS) {
+    if ($approval_settings == USER_REGISTER_VISITORS) {
       if ($this->userSettings->get('verify_mail')) {
         // No administrator approval required.
         _user_mail_notify('register_no_approval_required', $account);
       }
     }
     // Administrator approval required.
-    elseif ($approvalSettings == USER_REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL) {
+    elseif ($approval_settings == USER_REGISTER_VISITORS_ADMINISTRATIVE_APPROVAL) {
       _user_mail_notify('register_pending_approval', $account);
     }
-
-    return new ModifiedResourceResponse($account, 200);
   }
 
 }
diff --git a/core/modules/rest/src/ResourceAccessTrait.php b/core/modules/rest/src/ResourceAccessTrait.php
index 776caa6..00d8461 100644
--- a/core/modules/rest/src/ResourceAccessTrait.php
+++ b/core/modules/rest/src/ResourceAccessTrait.php
@@ -2,7 +2,7 @@
 
 namespace Drupal\rest;
 
-use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\FieldableEntityInterface;
 use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
 
 trait ResourceAccessTrait {
@@ -10,14 +10,14 @@
   /**
    * Performs edit access checks for fields.
    *
-   * @param \Drupal\Core\Entity\EntityInterface $entity
-   *   The entity object.
+   * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
+   *   Drupal\Core\Entity\FieldableEntityInterface
    *
    * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
    *   Throws access denied when the user does not have permissions to edit a
    *   field.
    */
-  protected function checkEditFieldAccess(EntityInterface $entity) {
+  protected function checkEditFieldAccess(FieldableEntityInterface $entity) {
     // Only check 'edit' permissions for fields that were actually submitted by
     // the user. Field access makes no difference between 'create' and 'update',
     // so the 'edit' operation is used here.
diff --git a/core/modules/rest/src/ResourceValidationTrait.php b/core/modules/rest/src/ResourceValidationTrait.php
index f8576a7..c1d667c 100644
--- a/core/modules/rest/src/ResourceValidationTrait.php
+++ b/core/modules/rest/src/ResourceValidationTrait.php
@@ -2,7 +2,7 @@
 
 namespace Drupal\rest;
 
-use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\FieldableEntityInterface;
 use Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException;
 
 trait ResourceValidationTrait {
@@ -10,13 +10,13 @@
   /**
    * Verifies that the whole entity does not violate any validation constraints.
    *
-   * @param \Drupal\Core\Entity\EntityInterface $entity
-   *   The entity object.
+   * @param \Drupal\Core\Entity\FieldableEntityInterface $entity
+   *   The entity fields are attached to.
    *
    * @throws \Symfony\Component\HttpKernel\Exception\UnprocessableEntityHttpException
    *   If validation errors are found.
    */
-  protected function validate(EntityInterface $entity) {
+  protected function validate(FieldableEntityInterface $entity) {
     $violations = $entity->validate();
 
     // Remove violations of inaccessible fields as they cannot stem from our