diff --git a/core/modules/user/src/AccountForm.php b/core/modules/user/src/AccountForm.php
index b157be34d0..0e35a52d1a 100644
--- a/core/modules/user/src/AccountForm.php
+++ b/core/modules/user/src/AccountForm.php
@@ -359,7 +359,7 @@ public function buildEntity(array $form, FormStateInterface $form_state) {
     //   numeric keys. Allow to override this per field. As this function is
     //   called twice, we have to prevent it from getting the array keys twice.
 
-    if (is_string(key($form_state->getValue('roles')))) {
+    if (is_string(key( (array) $form_state->getValue('roles')))) {
       $form_state->setValue('roles', array_keys(array_filter($form_state->getValue('roles'))));
     }