diff -u b/commerce_login_step.module b/commerce_login_step.module
--- b/commerce_login_step.module
+++ b/commerce_login_step.module
@@ -34,8 +34,14 @@
   // user is not logged in.
   if (!$user->uid && !empty($form['account'])) {
 
-    $existing_form_prefix = $form['#prefix'];
-    $existing_form_suffix = $form['#prefix'];
+    $existing_form_prefix = '';
+    if (isset($form['#prefix'])) {
+      $existing_form_prefix = $form['#prefix'];
+    }
+    $existing_form_suffix = '';
+    if (isset($form['#suffix'])) {
+      $existing_form_suffix = $form['#suffix'];
+    }
     $form['#prefix'] = '<div id="checkout-login-step">' . $existing_form_prefix;
     $form['#suffix'] = $existing_form_suffix . '</div>';
 
@@ -148 +154 @@
-}
+}
\ No newline at end of file