diff --git a/pkgs/tools/typesetting/lowdown/default.nix b/pkgs/tools/typesetting/lowdown/default.nix
index 8c55985a404c..e7280f06529e 100644
--- a/pkgs/tools/typesetting/lowdown/default.nix
+++ b/pkgs/tools/typesetting/lowdown/default.nix
@@ -27,7 +27,7 @@ stdenv.mkDerivation rec {
   '';
 
   # Fix lib extension so that fixDarwinDylibNames detects it
-  postInstall = lib.optionalString (stdenv.isDarwin) ''
+  postInstall = lib.optionalString stdenv.isDarwin ''
     mv $lib/lib/liblowdown.{so,dylib}
   '';