diff --git a/pkgs/tools/typesetting/asciidoc/default.nix b/pkgs/tools/typesetting/asciidoc/default.nix
index 83aa667f58fd..44c5f6d1f242 100644
--- a/pkgs/tools/typesetting/asciidoc/default.nix
+++ b/pkgs/tools/typesetting/asciidoc/default.nix
@@ -259,7 +259,7 @@ stdenv.mkDerivation rec {
   '';
 
   preInstall = "mkdir -p $out/etc/vim";
-  makeFlags = if stdenv.isCygwin then "DESTDIR=/." else null;
+  makeFlags = stdenv.lib.optional stdenv.isCygwin "DESTDIR=/.";
 
   meta = with stdenv.lib; {
     description = "Text-based document generation system";