diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index b6c531c..b4d0dd2 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -1080,6 +1080,14 @@ function drupal_page_is_cacheable($allow_caching = NULL) {
  * @see bootstrap_hooks()
  */
 function bootstrap_invoke_all($hook) {
+  // Prevent hook_boot() from being invoked more than once.
+  static $boot_invoked;
+  if ($hook == 'boot') {
+    if ($boot_invoked) {
+      return;
+    }
+    $boot_invoked = TRUE;
+  }
   // Bootstrap modules should have been loaded when this function is called, so
   // we don't need to tell module_list() to reset its internal list (and we
   // therefore leave the first parameter at its default value of FALSE). We
@@ -2401,7 +2409,12 @@ function _drupal_bootstrap_page_cache() {
     // Make sure there is a user object because its timestamp will be
     // checked, hook_boot might check for anonymous user etc.
     $user = drupal_anonymous_user();
-    // Get the page from the cache.
+    // If the skipping of the bootstrap hooks is not enforced, call
+    // hook_boot.
+    if (variable_get('page_cache_invoke_hooks', TRUE)) {
+      bootstrap_invoke_all('boot');
+    }
+    // Get the page from the cache. This checks drupal_page_is_cacheable().
     $cache = drupal_page_get_cache();
     // If there is a cached page, display it.
     if (is_object($cache)) {
@@ -2410,11 +2423,6 @@ function _drupal_bootstrap_page_cache() {
       $_GET['q'] = $cache->data['path'];
       drupal_set_title($cache->data['title'], PASS_THROUGH);
       date_default_timezone_set(drupal_get_user_timezone());
-      // If the skipping of the bootstrap hooks is not enforced, call
-      // hook_boot.
-      if (variable_get('page_cache_invoke_hooks', TRUE)) {
-        bootstrap_invoke_all('boot');
-      }
       drupal_serve_page_from_cache($cache);
       // If the skipping of the bootstrap hooks is not enforced, call
       // hook_exit.
@@ -2500,7 +2508,7 @@ function _drupal_bootstrap_variables() {
 }
 
 /**
- * Invokes hook_boot(), initializes locking system, and sends HTTP headers.
+ * Invokes hook_boot() and sends HTTP headers.
  */
 function _drupal_bootstrap_page_header() {
   bootstrap_invoke_all('boot');