diff --git a/uc_termsofservice.module b/uc_termsofservice.module
index 10934b4..4c81d00 100644
--- a/uc_termsofservice.module
+++ b/uc_termsofservice.module
@@ -335,7 +335,9 @@ function uc_termsofservice_form_alter(&$form, $form_state, $form_id) {
     return;
   }
   if ($form_id == 'uc_cart_checkout_form') {
-    $form['#validate'][] = 'uc_termsofservice_checkout_form_validate';
+    if (isset($form['panes']['uc_termsofservice_agreement_checkout'])) {
+      $form['#validate'][] = 'uc_termsofservice_checkout_form_validate';
+    }
     return;
   }
 }