diff --git a/pkgs/development/libraries/libxtc_dxtn/default.nix b/pkgs/development/libraries/libxtc_dxtn/default.nix
index 0e7442633d77..a23d74a2be86 100644
--- a/pkgs/development/libraries/libxtc_dxtn/default.nix
+++ b/pkgs/development/libraries/libxtc_dxtn/default.nix
@@ -8,8 +8,5 @@ stdenv.mkDerivation rec {
     sha256 = "0q5fjaknl7s0z206dd8nzk9bdh8g4p23bz7784zrllnarl90saa5";
   };
 
-  postUnpack = ''
-    tar xf ${mesa.src} --wildcards '*/include/'
-    export NIX_CFLAGS_COMPILE="-I $NIX_BUILD_TOP/[mM]esa*/include"
-  '';
+  NIX_CFLAGS_COMPILE = "-I ${mesa}/include";
 }