diff --git a/reference/mysqli/mysqli_stmt/affected-rows.xml b/reference/mysqli/mysqli_stmt/affected-rows.xml
index 59d9007742..ef383eca42 100644
--- a/reference/mysqli/mysqli_stmt/affected-rows.xml
+++ b/reference/mysqli/mysqli_stmt/affected-rows.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.2 $ -->
+<!-- $Revision: 1.3 $ -->
 <refentry xml:id="mysqli-stmt.affected-rows" xmlns="http://docbook.org/ns/docbook">
  <refnamediv>
   <refname>mysqli_stmt->affected_rows</refname>
@@ -49,6 +49,7 @@
    Zero indicates that no records where updated for an UPDATE/DELETE
    statement, no rows matched the WHERE clause in the query or that no query
    has yet been executed. -1 indicates that the query has returned an error.
+   NULL indicates an invalid argument was supplied to the function.
   </para>
   <note>
    <para>