diff --git a/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php b/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php
index 355591246..5fca066c6 100644
--- a/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php
+++ b/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php
@@ -37,6 +37,7 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
     if ($items[$delta]->query) {
       $default_url_value .= '?' . http_build_query($items[$delta]->query);
     }
+    $base_url = rtrim(Url::fromRoute('<front>', [], ['absolute' => TRUE])->toString(), '/');
     $element['path'] = [
       '#type' => 'textfield',
       '#title' => $this->t('Path'),
@@ -44,7 +45,9 @@ public function formElement(FieldItemListInterface $items, $delta, array $elemen
       '#default_value' => $default_url_value,
       '#maxlength' => 2048,
       '#required' => $element['#required'],
-      '#field_prefix' => Url::fromRoute('<front>', [], ['absolute' => TRUE])->toString(),
+      // Add a trailing slash to make it more clear that a redirect should not
+      // start with a leading slash.
+      '#field_prefix' => $base_url . '/',
       '#attributes' => ['data-disable-refocus' => 'true'],
     ];