diff --git a/modules/system/system.api.php b/modules/system/system.api.php
index 3be00dc..dd1eb77 100644
--- a/modules/system/system.api.php
+++ b/modules/system/system.api.php
@@ -2532,6 +2532,10 @@ function hook_requirements($phase) {
  * more tables and their related keys and indexes. A schema is defined by
  * hook_schema() which must live in your module's .install file.
  *
+ * This hook is called at both install and uninstall time, and in the latter
+ * case, it cannot rely on the .module file to be loaded or hooks to be known.
+ * If the .module file is needed, it may be loaded with drupal_load().
+ *
  * By implementing hook_schema() and specifying the tables your module
  * declares, you can easily create and drop these tables on all
  * supported database engines. You don't have to deal with the
@@ -2694,7 +2698,8 @@ function hook_query_TAG_alter(QueryAlterableInterface $query) {
  * be created before this hook is fired.
  *
  * Implementations of this hook are by convention declared in the module's
- * .install file. The hook will only be called the first time a module is
+ * .install file,  but the implementation can rely on the .module file being
+ * loaded. The hook will only be called the first time a module is
  * enabled or after it is re-enabled after being uninstalled. The module's
  * schema version will be set to the module's greatest numbered update hook.
  * Because of this, any time a hook_update_N() is added to the module, this
@@ -2951,7 +2956,8 @@ function hook_uninstall() {
  * Perform necessary actions after module is enabled.
  *
  * The hook is called every time the module is enabled. It should be
- * implemented in the module's .install file.
+ * implemented in the module's .install file, but the implementation can
+ * rely on the .module file being loaded.
  *
  * @see module_enable()
  * @see hook_install()
@@ -2965,7 +2971,8 @@ function hook_enable() {
  * Perform necessary actions before module is disabled.
  *
  * The hook is called every time the module is disabled. It should be
- * implemented in the module's .install file.
+ * implemented in the module's .install file, but the implementation can rely
+ * on the .module file being loaded.
  *
  * @see hook_uninstall()
  * @see hook_modules_disabled()