diff --git a/doc/shepherd.texi b/doc/shepherd.texi
index 18f1a4d..696477e 100644
--- a/doc/shepherd.texi
+++ b/doc/shepherd.texi
@@ -967,7 +967,7 @@ immediately before invoking @var{command}.  @var{user} may be a string,
 indicating a user name, or a number, indicating a user ID.  Likewise,
 @var{command} will be run under the current group, unless the
 @var{group} keyword argument is present and not false, and
-supplementary-groups is not '().
+@var{supplementary-groups} is not @code{'()}.
 
 @code{fork+exec-command} does the same as @code{exec-command}, but in
 a separate process whose PID it returns.