diff --git a/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php b/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php
index 0aeffeb..81f5cca 100644
--- a/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php
+++ b/src/Plugin/Field/FieldWidget/RedirectSourceWidget.php
@@ -46,7 +46,9 @@ class RedirectSourceWidget extends WidgetBase {
       '#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' => Url::fromRoute('<front>', [], ['absolute' => TRUE])->toString() . '/',
       '#attributes' => ['data-disable-refocus' => 'true'],
     ];