diff --git a/modules/block/block.module b/modules/block/block.module
index ff77d9e..6fed57b 100644
--- a/modules/block/block.module
+++ b/modules/block/block.module
@@ -836,19 +836,41 @@ function block_block_list_alter(&$blocks) {
  *   An array of visible blocks as expected by drupal_render().
  */
 function _block_render_blocks($region_blocks) {
-  // Block caching is not compatible with node access modules. We also
-  // preserve the submission of forms in blocks, by fetching from cache only
-  // if the request method is 'GET' (or 'HEAD').
-  $cacheable = !count(module_implements('node_grants')) && ($_SERVER['REQUEST_METHOD'] == 'GET' || $_SERVER['REQUEST_METHOD'] == 'HEAD');
+  // Block caching is not compatible with node access modules by default but
+  // could be override. We also preserve the submission of forms in blocks, by
+  // fetching from cache only if the request method is 'GET' (or 'HEAD').
+  $cacheable = (variable_get('block_cache_bypass_node_grants', FALSE) || !count(module_implements('node_grants'))) && ($_SERVER['REQUEST_METHOD'] == 'GET' || $_SERVER['REQUEST_METHOD'] == 'HEAD');
+
+  // Proceed to a loop over all blocks in order to compute their respective
+  // cache identifiers, this allows us to do one single cache_get_multiple()
+  // call instead of doing one cache_get() call per block.
+  $cached_blocks = array();
+  if ($cacheable) {
+
+    $cids = array();
+    foreach ($region_blocks as $key => $block) {
+      if (!isset($block->content)) {
+        if (($cid = _block_get_cache_id($block))) {
+          $cids[] = $cid;
+        }
+      }
+    }
+
+    if ($cids) {
+      $cached_blocks = cache_get_multiple($cids, 'cache_block');
+    }
+  }
+
   foreach ($region_blocks as $key => $block) {
     // Render the block content if it has not been created already.
     if (!isset($block->content)) {
       // Erase the block from the static array - we'll put it back if it has
       // content.
       unset($region_blocks[$key]);
-      // Try fetching the block from cache.
-      if ($cacheable && ($cid = _block_get_cache_id($block)) && ($cache = cache_get($cid, 'cache_block'))) {
-        $array = $cache->data;
+
+      // Try fetching the block from the previously loaded cache entries.
+      if (($cid = _block_get_cache_id($block)) && isset($cached_blocks[$cid])) {
+        $array = $cached_blocks[$cid]->data;
       }
       else {
         $array = module_invoke($block->module, 'block_view', $block->delta);
@@ -1013,13 +1035,13 @@ function block_menu_delete($menu) {
  * Implements hook_form_FORM_ID_alter().
  */
 function block_form_system_performance_settings_alter(&$form, &$form_state) {
-  $disabled = count(module_implements('node_grants'));
+  $disabled = (variable_get('block_cache_bypass_node_grants', FALSE) || count(module_implements('node_grants')));
   $form['caching']['block_cache'] = array(
     '#type' => 'checkbox',
     '#title' => t('Cache blocks'),
     '#default_value' => variable_get('block_cache', FALSE),
     '#disabled' => $disabled,
-    '#description' => $disabled ? t('Block caching is inactive because you have enabled modules defining content access restrictions.') : NULL,
+    '#description' => $disabled ? t('Block caching is inactive because you have enabled modules defining content access restrictions.') . ' '. t('You can force block caching to be enabled by setting the <em>block_cache_bypass_node_grants</em> variable to TRUE, see the <em>settings.php</em> file.') : NULL,
     '#weight' => -1,
   );
 }
diff --git a/sites/default/default.settings.php b/sites/default/default.settings.php
index 40f552e..d84b460 100644
--- a/sites/default/default.settings.php
+++ b/sites/default/default.settings.php
@@ -433,6 +433,19 @@ ini_set('session.cookie_lifetime', 2000000);
 # $conf['js_gzip_compression'] = FALSE;
 
 /**
+ * Block caching:
+ *
+ * Block caching may not compatible with node access modules depending on
+ * how the original block cache policy is defined set by the module that
+ * provides the block. By default, block cache will be disabled when one or
+ * more modules implement the hook_node_grant() hook. If you consider block
+ * caching to be safe on your site, you can bypass this restriction and force
+ * block caching to the default policy (per block setting) by setting the
+ * following variable to TRUE.
+ */
+# $conf['block_cache_bypass_node_grants'] = TRUE;
+
+/**
  * String overrides:
  *
  * To override specific strings on your site with or without enabling the Locale