diff --git a/includes/common.inc b/includes/common.inc
index cd30145..e641429 100644
--- a/includes/common.inc
+++ b/includes/common.inc
@@ -5210,6 +5210,11 @@ function _drupal_bootstrap_full() {
   unicode_check();
   // Undo magic quotes
   fix_gpc_magic();
+  // Reset drupal_alter() and module_implements() static caches as these
+  // include implementations for vital modules only when called early on
+  // in the bootstrap.
+  drupal_static_reset('drupal_alter');
+  drupal_static_reset('module_implements');
   // Load all enabled modules
   module_load_all();
   // Make sure all stream wrappers are registered.
diff --git a/includes/module.inc b/includes/module.inc
index 494924f..8b2e324 100644
--- a/includes/module.inc
+++ b/includes/module.inc
@@ -699,6 +699,10 @@ function module_implements($hook, $sort = FALSE, $reset = FALSE) {
   }
   $implementations = &$drupal_static_fast['implementations'];
 
+  if (drupal_get_bootstrap_phase() != DRUPAL_BOOTSTRAP_FULL && (!defined('MAINTENANCE_MODE') || (MAINTENANCE_MODE != 'update' && MAINTENANCE_MODE != 'install'))) {
+    trigger_error('module_implements() should not be called before full bootstrap.', E_USER_WARNING);
+  }
+
   // We maintain a persistent cache of hook implementations in addition to the
   // static cache to avoid looping through every module and every hook on each
   // request. Benchmarks show that the benefit of this caching outweighs the