Index: uc_cart.module
===================================================================
--- uc_cart.module	(revision 404)
+++ uc_cart.module	(working copy)
@@ -403,13 +403,20 @@
     case 'view':
       // 0 = Default shopping cart block.
       if ($delta == 0) {
-        $cachable = !$user->uid && variable_get('cache', CACHE_DISABLED) != CACHE_DISABLED;
+        if (function_exists('drupal_page_is_cacheable')) {
+          $cachable = drupal_page_is_cacheable();
+          $is_pressflow = TRUE;
+        }
+        else {
+          $cachable = !$user->uid && variable_get('cache', CACHE_DISABLED) != CACHE_DISABLED;
+        }
+
         $uc_cart_path = drupal_get_path('module', 'uc_cart');
         $product_count = count(uc_cart_get_contents());
 
         // Display nothing if the block is set to hide on empty and there are no
         // items in the cart.
-        if (!$cachable && variable_get('uc_cart_block_empty_hide', FALSE) && !$product_count) {
+        if ((!$cacheable || !empty($is_pressflow)) && variable_get('uc_cart_block_empty_hide', FALSE) && !$product_count) {
           return;
         }