diff --git a/pkgs/development/libraries/libfaketime/default.nix b/pkgs/development/libraries/libfaketime/default.nix
index cc9db8f7e661..65d04cb53f16 100644
--- a/pkgs/development/libraries/libfaketime/default.nix
+++ b/pkgs/development/libraries/libfaketime/default.nix
@@ -21,9 +21,8 @@ stdenv.mkDerivation rec {
     done
   '';
 
-  preBuild = ''
-    makeFlagsArray+=(PREFIX="$out" LIBDIRNAME=/lib)
-  '';
+  PREFIX = placeholder "out";
+  LIBDIRNAME = "/lib";
 
   checkInputs = [ perl ];