diff --git a/core/modules/system/src/Plugin/Condition/RequestPath.php b/core/modules/system/src/Plugin/Condition/RequestPath.php
index 17373ce..55e08e0 100644
--- a/core/modules/system/src/Plugin/Condition/RequestPath.php
+++ b/core/modules/system/src/Plugin/Condition/RequestPath.php
@@ -116,6 +116,22 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
   /**
    * {@inheritdoc}
    */
+  public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
+    $paths = explode("\r\n", $form_state->getValue('pages'));
+    foreach ($paths as $path) {
+      if (empty($path) || $path === '<front>' || strpos($path, '/') === 0) {
+        continue;
+      }
+      else {
+        $form_state->setErrorByName('pages', $this->t('Paths require a leading forward slash when used with the Pages setting.'));
+        return;
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
     $this->configuration['pages'] = $form_state->getValue('pages');
     parent::submitConfigurationForm($form, $form_state);