diff --git a/pkgs/tools/text/ispell/default.nix b/pkgs/tools/text/ispell/default.nix
index d35a3d61b1b..dbec8d353d9 100644
--- a/pkgs/tools/text/ispell/default.nix
+++ b/pkgs/tools/text/ispell/default.nix
@@ -22,8 +22,8 @@ stdenv.mkDerivation rec {
     ./patches/0030-Display-whole-multibyte-character.patch
   ];
   postPatch = ''
-    if [ ! stdenv.isDarwin ]; then echo "#define USG" >> local.h; fi
     cat >> local.h <<EOF
+    ${stdenv.lib.optionalString (!stdenv.isDarwin) "#define USG"}
     #define TERMLIB "-lncurses"
     #define LANGUAGES "{american,MASTERDICTS=american.med,HASHFILES=americanmed.hash}"
     #define MASTERHASH "americanmed.hash"