diff --git a/doc/manual/command-ref/conf-file.xml b/doc/manual/command-ref/conf-file.xml
index d2c9145e0505b52a43ddf218130b7c899c3ed48d..6c0af39ecda9f3717aba3c9f49a07449d825f429 100644
--- a/doc/manual/command-ref/conf-file.xml
+++ b/doc/manual/command-ref/conf-file.xml
@@ -18,7 +18,8 @@
 <refsection><title>Description</title>
 
 <para>A number of persistent settings of Nix are stored in the file
-<filename><replaceable>sysconfdir</replaceable>/nix/nix.conf</filename>.
+<filename><replaceable>sysconfdir</replaceable>/nix/nix.conf</filename> or
+<filename>$NIX_CONF_DIR/nix.conf</filename> if <envar>NIX_CONF_DIR</envar> is set.
 This file is a list of <literal><replaceable>name</replaceable> =
 <replaceable>value</replaceable></literal> pairs, one per line.
 Comments start with a <literal>#</literal> character.  Here is an example