diff --git a/user_guide_src/source/installation/upgrade_300.rst b/user_guide_src/source/installation/upgrade_300.rst
index 497dc72..78333c9 100644
--- a/user_guide_src/source/installation/upgrade_300.rst
+++ b/user_guide_src/source/installation/upgrade_300.rst
@@ -168,6 +168,21 @@
     `Session Metadata <../libraries/sessions.html#accessing-session-metadata>`_
     if your application relies on those values.
 
+  - Check ``unset_userdata()`` usage
+
+    Previously, this method used to accept an associative array of
+    ``'key' => 'dummy value'`` pairs for unsetting multiple keys. That
+    however makes no sense and you now have to pass *only* the keys, as
+    the elements of an array.
+
+    ::
+
+    	// Old
+    	$this->session->unset_userdata(array('item' => '', 'item2' => ''));
+
+    	// New
+    	$this->session->unset_userdata(array('item', 'item2'));
+
 Finally, if you have written a Session extension, you must now move it to
 the *application/libraries/Session/* directory, although chances are that
 it will now also have to be re-factored.
diff --git a/user_guide_src/source/libraries/sessions.rst b/user_guide_src/source/libraries/sessions.rst
index 6395c06..91dafde 100644
--- a/user_guide_src/source/libraries/sessions.rst
+++ b/user_guide_src/source/libraries/sessions.rst
@@ -203,12 +203,16 @@
 
 	$this->session->unset_userdata('some_name');
 
-This method also accepts an associative array of items to unset::
+This method also accepts an array of item keys to unset::
 
-	$array_items = array('username' => '', 'email' => '');
+	$array_items = array('username', 'email');
 
 	$this->session->unset_userdata($array_items);
 
+.. note:: In previous versions, the ``unset_userdata()`` method used
+	to accept an associative array of ``key => 'dummy value'``
+	pairs. This is no longer supported.
+
 Flashdata
 =========