diff --git a/doc/stdenv.xml b/doc/stdenv.xml
index e0d97e42e4c..68f07bfe21e 100644
--- a/doc/stdenv.xml
+++ b/doc/stdenv.xml
@@ -1076,6 +1076,17 @@ passthru = {
       </para>
      </listitem>
     </varlistentry>
+    <varlistentry>
+     <term>
+      <varname>prefixKey</varname>
+     </term>
+     <listitem>
+      <para>
+       The key to use when specifying the prefix. By default, this is set to
+       <option>--prefix=</option> as that is used by the majority of packages.
+      </para>
+     </listitem>
+    </varlistentry>
     <varlistentry>
      <term>
       <varname>dontAddDisableDepTrack</varname>