diff --git a/uc_taxes/uc_taxes.module b/uc_taxes/uc_taxes.module
index a1d8322..38224cd 100644
--- a/uc_taxes/uc_taxes.module
+++ b/uc_taxes/uc_taxes.module
@@ -238,50 +238,59 @@ function uc_line_item_tax($op, $order) {
 /**
  * Handles the line item subtotal before taxes.
  */
-function uc_line_item_tax_subtotal($op, $order) {
+function uc_line_item_tax_subtotal($op, $arg1) {
   $amount = 0;
-  $has_taxes = FALSE;
-  $different = FALSE;
 
-  if (is_array($order->products)) {
-    foreach ($order->products as $item) {
-      $amount += $item->price * $item->qty;
-    }
-  }
-  if (is_array($order->line_items)) {
-    foreach ($order->line_items as $key => $line_item) {
-      if ($line_item['type'] == 'subtotal') {
-        continue;
-      }
-      if (substr($line_item['type'], 0, 3) != 'tax') {
-        $amount += $line_item['amount'];
-        $different = TRUE;
-      }
-      else {
-        $has_taxes = TRUE;
+  switch ($op) {
+    case 'cart-preview':
+      if (!empty($arg1)) {
+        foreach ($arg1 as $item) {
+          $amount += $item->price * $item->qty;
+        }
       }
-    }
-  }
-  if (isset($order->taxes) && is_array($order->taxes)) {
-    $has_taxes = TRUE;
-  }
-  if ($different && $has_taxes) {
-    switch ($op) {
-      case 'cart-preview':
+      if (!empty($amount)) {
         drupal_add_js("if (Drupal.jsEnabled) { \$(document).ready(function() {
           if (window.set_line_item) {
             set_line_item('tax_subtotal', '". t('Subtotal excluding taxes') ."', ". $amount .", ". variable_get('uc_li_tax_subtotal_weight', 8) .");
           }
         })};", 'inline');
+      }
       break;
-      case 'load':
+
+    case 'load':
+      $order = $arg1;
+      $has_taxes = FALSE;
+      $different = FALSE;
+      if (!empty($order->taxes) && is_array($order->taxes)) {
+        $has_taxes = TRUE;
+      }
+      if (is_array($order->products)) {
+        foreach ($order->products as $item) {
+          $amount += $item->price * $item->qty;
+        }
+      }
+      if (!empty($order->line_items) && is_array($order->line_items)) {
+        foreach ($order->line_items as $key => $line_item) {
+          if ($line_item['type'] == 'subtotal') {
+            continue;
+          }
+          if (substr($line_item['type'], 0, 3) != 'tax') {
+            $amount += $line_item['amount'];
+            $different = TRUE;
+          }
+          else {
+            $has_taxes = TRUE;
+          }
+        }
+      }
+      if ($different && $has_taxes) {
         return array(array(
           'id' => 'tax_subtotal',
           'title' => t('Subtotal excluding taxes'),
           'amount' => $amount,
           'weight' => variable_get('uc_li_tax_subtotal_weight', 7),
         ));
-    }
+      }
   }
 }