diff --git a/nixos/doc/manual/development/option-types.xml b/nixos/doc/manual/development/option-types.xml
index 7969d8124738..5cb747e6d9f1 100644
--- a/nixos/doc/manual/development/option-types.xml
+++ b/nixos/doc/manual/development/option-types.xml
@@ -21,6 +21,15 @@
   </para>
 
   <variablelist>
+   <varlistentry>
+    <term><varname>types.attrs</varname>
+    </term>
+    <listitem>
+     <para>
+      A free-form attribute set.
+     </para>
+    </listitem>
+   </varlistentry>
    <varlistentry>
     <term><varname>types.bool</varname>
     </term>