diff --git a/core/modules/block/src/BlockForm.php b/core/modules/block/src/BlockForm.php
index 4bc3271..8f33017 100644
--- a/core/modules/block/src/BlockForm.php
+++ b/core/modules/block/src/BlockForm.php
@@ -166,7 +166,7 @@ public function form(array $form, FormStateInterface $form_state) {
       $form['theme'] = [
         '#type' => 'select',
         '#options' => $theme_options,
-        '#title' => t('Theme'),
+        '#title' => $this->t('Theme'),
         '#default_value' => $theme,
         '#ajax' => [
           'callback' => '::themeSwitch',