Index: includes/bootstrap.inc
===================================================================
--- includes/bootstrap.inc	(revision 9369)
+++ includes/bootstrap.inc	(working copy)
@@ -965,12 +965,14 @@
     }
   }
   elseif ($phase == DRUPAL_BOOTSTRAP_LATE_PAGE_CACHE) {
-    if ($cache = page_get_cache()) {
-      if (variable_get('cache', CACHE_DISABLED) == CACHE_AGGRESSIVE) {
+    if (variable_get('cache', CACHE_DISABLED) == CACHE_AGGRESSIVE) {
+      if ($cache = page_get_cache()) {
         drupal_page_cache_header($cache);
         exit();
       }
-      elseif (variable_get('cache', CACHE_DISABLED) == CACHE_NORMAL) {
+    }
+    elseif (variable_get('cache', CACHE_DISABLED) == CACHE_NORMAL) {
+      if ($cache = page_get_cache()) {
         require_once './includes/module.inc';
         bootstrap_invoke_all('init');
         drupal_page_cache_header($cache);
@@ -978,6 +980,12 @@
         exit();
       }
     }
+    else {
+      // Caching is disabled so we can simply call ob_start() instead
+      // of the expensive page_get_cache()
+      ob_start();
+    }
+
     require_once './includes/module.inc';
   }
 }