diff --git a/builder.nix b/builder.nix
index e386aea..5f5d926 100644
--- a/builder.nix
+++ b/builder.nix
@@ -1,4 +1,4 @@
-buildArgs@{ lib ? import ./lib.nix {}, nixpkgs ? <nixpkgs>, pkgs ? import nixpkgs {} }:
+buildArgs@{ lib ? import ./lib.nix {}, nixpkgs ? <nixpkgs>, pkgs ? import nixpkgs {}, root, filter ? [] }:
 let
   inherit (lib) searchPath whichdo d1 d2;
 
@@ -22,6 +22,9 @@ let
       in if imported.success
          then imported.value
          else {
+           src = filterSource
+             (path: type: type != "directory" || (baseNameOf path != ".git" && (all (x: trace x path != x) filter)))
+             (/. + root);
            builder = ''
              #!/bin/sh
              set -e
diff --git a/nixredo b/nixredo
index 2e5285b..953d38c 100644
--- a/nixredo
+++ b/nixredo
@@ -1,14 +1,24 @@
 #!/bin/sh
 exec >&2
+[ "${S+x}" = x ] || { printf "Set S to the root location of your source tree\n"; exit 127; }
 [ "${NIXREDO_ROOT-x}" != x ] || { printf "Set NIXREDO_ROOT. Set empty to use global nix store\n"; exit 127; }
 if [ $# -eq 0 ]; then set -- all; fi
+
+S=$(realpath -s "$S")
+
+if [ "${NIXREDO_ROOT#$S}" != "${NIXREDO_ROOT}" ]; then
+    filter=$(realpath -s "${NIXREDO_ROOT}")
+else
+    filter=
+fi
+
 set -e
 set -- "$1" "$1" "$1.redo.tmp"
 f=$(realpath -s "$1")
 out=$(nix -vL --show-trace build ${NIXREDO_ROOT:+--store "$NIXREDO_ROOT"} \
           --option auto-optimise-store true --option substituters daemon \
           --impure --json --no-link \
-          --expr " import @buildernix@ { lib = import @libnix@ {}; } \"$f\"" |
+          --expr " import @buildernix@ { lib = import @libnix@ {}; root =\"$S\"; filter = [ \"$filter\" ]; } \"$f\"" |
           @jq@ -r '.[0].outputs.out')
 [ -n "$out" ] || exit 127
 rm -rf "$3"