diff --git a/includes/cache.inc b/includes/cache.inc
index 590592d..70bbbb0 100644
--- a/includes/cache.inc
+++ b/includes/cache.inc
@@ -97,55 +97,103 @@ function _views_fetch_plugin_data($type = NULL, $plugin = NULL, $reset = FALSE)
  */
 function _views_discover_default_views($reset = FALSE) {
   static $cache = NULL;
+  $lock_name = __FUNCTION__;
 
-  if (!isset($cache) || $reset) {
+  if (!$reset && !isset($cache)) {
     $index = views_cache_get('views_default_views_index', TRUE);
 
+    $rebuild_cache = TRUE;
     // Retrieve each cached default view
-    if (!$reset && isset($index->data) && is_array($index->data)) {
+    if (isset($index->data) && is_array($index->data)) {
+      $rebuild_cache = FALSE;
       $cache = array();
       foreach ($index->data as $view_name) {
-        $data = views_cache_get('views_default:' . $view_name, TRUE);
-        if (isset($data->data) && is_object($data->data)) {
-          $cache[$view_name] = $data->data;
+        $cid = 'views_default:' . $view_name;
+        if ($cached = views_cache_get($cid, TRUE)) {
+          $cache[$view_name] = $cached->data;
+        }
+        else {
+          // As soon as there is a cache miss on one item, try to acquire a
+          // lock.
+          if (!$lock_acquired = lock_acquire($lock_name)) {
+            lock_wait($lock_name, 2);
+            // After waiting, try to fetch the default view from cache again.
+            // If available another process may have rebuilt it, so do not
+            // attempt to rebuild the cache.
+            if ($cached = views_cache_get($cid, TRUE)) {
+              $cache[$view_name] = $cached->data;
+            }
+            // If the item is still not in the cache, try to acquire the lock
+            // again and rebuild the cache.
+            else {
+              $lock_acquired = lock_acquire($lock_name);
+              $rebuild_cache = TRUE;
+              break;
+            }
+          }
+          // If the lock was acquired, always rebuild the cache.
+          else {
+            $rebuild_cache = TRUE;
+            break;
+          }
         }
       }
     }
-    // If missing index, rebuild the cache
     else {
-      views_include_default_views();
-      $cache = array();
-
-      foreach (module_implements('views_default_views') as $module) {
-        $results = call_user_func($module . "_views_default_views");
-        if (!empty($results) && is_array($results)) {
-          foreach($results as $name => $view) {
-            // Only views with a sufficiently high api version are eligible.
-            if (!empty($view->api_version) && $view->api_version >= 2) {
-              // Do not cache dead handlers.
-              $view->destroy();
-              if (!isset($cache[$name])) {
-                $cache[$name] = $view;
-              }
-              else {
-                watchdog('view', "View name '@name' is already taken", array('@name' => $name), WATCHDOG_ERROR);
-              }
+      if (!$lock_acquired = lock_acquire($lock_name)) {
+        lock_wait($lock_name, 2);
+        if ($cached = views_cache_get('views_default_views_index', TRUE)) {
+          // Another process has rebuilt the cache while we waited. Re-run the
+          // function to avoid a full cache rebuild.
+          $cache = _views_discover_default_views();
+          $rebuild_cache = FALSE;
+        }
+        else {
+          // Continue with the rebuild.
+          $rebuild_cache = TRUE;
+        }
+      }
+    }
+  }
+  if ($reset || $rebuild_cache) {
+    views_include_default_views();
+    $cache = array();
+
+    foreach(module_implements('views_default_views') as $module) {
+      $results = call_user_func($module . "_views_default_views");
+      if (!empty($results) && is_array($results)) {
+        foreach($results as $name => $view) {
+          // Only views with a sufficiently high api version are eligible.
+          if (!empty($view->api_version) && $view->api_version >= 2) {
+            // Do not cache dead handlers.
+            $view->destroy();
+            if (!isset($cache[$name])) {
+              $cache[$name] = $view;
+            }
+            else {
+              watchdog('view', "View name '@name' is already taken", array('@name' => $name), WATCHDOG_ERROR);
             }
           }
         }
       }
+    }
+
+    // Allow modules to modify default views before they are cached.
+    drupal_alter('views_default_views', $cache);
 
-      // Allow modules to modify default views before they are cached.
-      drupal_alter('views_default_views', $cache);
+    // Only set the cache if we already have a lock, are able to acquire one, or
+    // if a reset was explicitly requested.
 
-      // Cache the index
+    if (!empty($lock_acquired) || lock_acquire($lock_name) || $reset) {
+      // Cache the index.
       $index = array_keys($cache);
       views_cache_set('views_default_views_index', $index, TRUE);
 
-      // Cache each view
+      // Cache each view.
       foreach ($cache as $name => $view) {
         views_cache_set('views_default:' . $name, $view, TRUE);
       }
+      lock_release($lock_name);
     }
   }