diff --git a/src/Plugin/search_api/processor/Tokenizer.php b/src/Plugin/search_api/processor/Tokenizer.php
index 3b6c0b61..a58d9b28 100644
--- a/src/Plugin/search_api/processor/Tokenizer.php
+++ b/src/Plugin/search_api/processor/Tokenizer.php
@@ -95,8 +95,8 @@ public function validateConfigurationForm(array &$form, FormStateInterface $form
     parent::validateConfigurationForm($form, $form_state);
 
     $spaces = str_replace('/', '\/', trim($form_state->getValues()['spaces']));
-    if ($spaces !== '' && @preg_match('/(' . $spaces . ')+/u', '') === FALSE) {
-      $form_state->setError($form['spaces'], $form['spaces']['#title'] . ': ' . $this->t('The entered text is no valid regular expression.'));
+    if ($spaces !== '' && @preg_match('/[' . $spaces . ']+/u', '') === FALSE) {
+      $form_state->setError($form['spaces'], $form['spaces']['#title'] . ': ' . $this->t('The entered text is no valid PCRE character class.'));
     }
   }