diff --git a/pkgs/development/tools/misc/arcanist/default.nix b/pkgs/development/tools/misc/arcanist/default.nix
index a8e779347d8..e55faaa1e63 100644
--- a/pkgs/development/tools/misc/arcanist/default.nix
+++ b/pkgs/development/tools/misc/arcanist/default.nix
@@ -24,6 +24,7 @@ stdenv.mkDerivation rec {
     ORIG=`pwd`
     cp -R ${libphutil} libphutil
     cp -R ${arcanist} arcanist
+    chmod +w -R libphutil arcanist
     cd libphutil/support/xhpast
     make clean all install
     cd $ORIG