diff --git a/pkgs/applications/networking/sync/unison/default.nix b/pkgs/applications/networking/sync/unison/default.nix
index 535757503ca..7b7318544c5 100644
--- a/pkgs/applications/networking/sync/unison/default.nix
+++ b/pkgs/applications/networking/sync/unison/default.nix
@@ -1,4 +1,4 @@
-{stdenv, fetchFromGitHub, ocamlPackages, fontschumachermisc, xset, makeWrapper, ncurses
+{stdenv, fetchFromGitHub, ocamlPackages, fontschumachermisc, xset, makeWrapper, ncurses, gnugrep
 , enableX11 ? true}:
 
 let inherit (ocamlPackages) ocaml lablgtk; in
@@ -38,7 +38,7 @@ stdenv.mkDerivation (rec {
   postInstall = if enableX11 then ''
     for i in $(cd $out/bin && ls); do
       wrapProgram $out/bin/$i \
-        --run "[ -n \"\$DISPLAY\" ] && (${xset}/bin/xset q | grep -q \"${fontschumachermisc}\" || ${xset}/bin/xset +fp \"${fontschumachermisc}/lib/X11/fonts/misc\")"
+        --run "[ -n \"\$DISPLAY\" ] && (${xset}/bin/xset q | ${gnugrep}/bin/grep -q \"${fontschumachermisc}\" || ${xset}/bin/xset +fp \"${fontschumachermisc}/lib/X11/fonts/misc\")"
     done
   '' else "";