diff --git a/default.nix b/default.nix
index 0b33fdcc..5e712771 100644
--- a/default.nix
+++ b/default.nix
@@ -40,7 +40,7 @@ let
           xo-cmake          = self.callPackage pkgs/xo-cmake.nix          {};
           xo-indentlog      = self.callPackage pkgs/xo-indentlog.nix      {};
           xo-refcnt         = self.callPackage pkgs/xo-refcnt.nix         {};
-#          xo-subsys         = self.callPackage pkgs/xo-subsys.nix         {};
+          xo-subsys         = self.callPackage pkgs/xo-subsys.nix         {};
 #          xo-randomgen      = self.callPackage pkgs/xo-randomgen.nix      {};
 #          xo-ordinaltree    = self.callPackage pkgs/xo-ordinaltree.nix    {};
 #          xo-pyutil         = self.callPackage pkgs/xo-pyutil.nix         {};
diff --git a/pkgs/xo-subsys.nix b/pkgs/xo-subsys.nix
new file mode 100644
index 00000000..59d0fef0
--- /dev/null
+++ b/pkgs/xo-subsys.nix
@@ -0,0 +1,20 @@
+{
+  # nixpkgs dependencies
+  stdenv, cmake, catch2,
+
+  # xo dependencies
+  xo-cmake,
+
+} :
+
+stdenv.mkDerivation (finalattrs:
+  {
+    name = "xo-subsys";
+    version = "1.0";
+
+    src = ../xo-subsys;
+
+    cmakeFlags = ["-DCMAKE_MODULE_PATH=${xo-cmake}/share/cmake"];
+    #doCheck = true;
+    nativeBuildInputs = [ cmake catch2 xo-cmake ];
+  })
diff --git a/pkgs/xo-userenv.nix b/pkgs/xo-userenv.nix
index 9ec8008c..da6f68c7 100644
--- a/pkgs/xo-userenv.nix
+++ b/pkgs/xo-userenv.nix
@@ -25,7 +25,7 @@
   xo-cmake,
   xo-indentlog,
   xo-refcnt,
-#  xo-subsys,
+  xo-subsys,
 #  xo-randomgen,
 #  xo-ordinaltree,
 #  xo-flatstring,
@@ -60,7 +60,7 @@ buildEnv {
   paths = [ xo-cmake
             xo-indentlog
             xo-refcnt
-#            xo-subsys
+            xo-subsys
 #            xo-randomgen
 #            xo-ordinaltree
 #            xo-pyutil