diff --git a/.github/workflows/main-stock-ubuntu.yml b/.github/workflows/main-stock-ubuntu.yml
index ab03c76f..4516ac3b 100644
--- a/.github/workflows/main-stock-ubuntu.yml
+++ b/.github/workflows/main-stock-ubuntu.yml
@@ -102,6 +102,11 @@ jobs:
           echo "::group::xo-pyunit build"
           cmake --build .build -- xo-pyunit
 
+          ##############
+
+          echo "::group::xo-expression build"
+          cmake --build .build -- xo-expression
+
           echo "::group::xo build (catch all)"
           cmake --build .build #--verbose
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4287923a..dca4d8de 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -78,7 +78,7 @@ add_subdirectory(xo-pyreflect)
 add_subdirectory(xo-ratio)
 add_subdirectory(xo-unit)
 add_subdirectory(xo-pyunit)
-#add_subdirectory(xo-expression)
+add_subdirectory(xo-expression)
 #add_subdirectory(xo-pyexpression)
 #add_subdirectory(xo-tokenizer)
 #add_subdirectory(xo-reader)
diff --git a/default.nix b/default.nix
index 533f8014..b608a335 100644
--- a/default.nix
+++ b/default.nix
@@ -51,7 +51,8 @@ let
           xo-ratio          = self.callPackage pkgs/xo-ratio.nix          {};
           xo-unit           = self.callPackage pkgs/xo-unit.nix           {};
           xo-pyunit         = self.callPackage pkgs/xo-pyunit.nix         {};
-#          xo-expression     = self.callPackage pkgs/xo-expression.nix     {};
+
+          xo-expression     = self.callPackage pkgs/xo-expression.nix     {};
 #          xo-pyexpression   = self.callPackage pkgs/xo-pyexpression.nix   {};
 #          xo-tokenizer      = self.callPackage pkgs/xo-tokenizer.nix      {};
 #          xo-reader         = self.callPackage pkgs/xo-reader.nix         {};
diff --git a/pkgs/xo-expression.nix b/pkgs/xo-expression.nix
new file mode 100644
index 00000000..c311fd06
--- /dev/null
+++ b/pkgs/xo-expression.nix
@@ -0,0 +1,21 @@
+{
+  # dependencies
+  stdenv, cmake, catch2,
+
+  xo-cmake, xo-reflect,
+} :
+
+stdenv.mkDerivation (finalattrs:
+  {
+    name = "xo-expression";
+    version = "1.0";
+
+    src = ../xo-expression;
+
+    cmakeFlags = ["-DCMAKE_MODULE_PATH=${xo-cmake}/share/cmake"];
+    doCheck = true;
+    propagatedBuildInputs = [ xo-reflect ];
+    nativeBuildInputs = [ cmake catch2
+                          xo-cmake
+                        ];
+  })
diff --git a/pkgs/xo-userenv.nix b/pkgs/xo-userenv.nix
index 655017f7..60782bf8 100644
--- a/pkgs/xo-userenv.nix
+++ b/pkgs/xo-userenv.nix
@@ -35,7 +35,8 @@
   xo-pyreflect,
   xo-ratio,
   xo-unit,
-#  xo-pyunit,
+  xo-pyunit,
+
 #  xo-printjson,
 #  xo-pyprintjson,
 #  xo-callback,
@@ -46,7 +47,9 @@
 #  xo-simulator,
 #  xo-pysimulator, xo-distribution, xo-pydistribution, xo-process, xo-pyprocess, xo-statistics, xo-kalmanfilter,
 #  xo-pykalmanfilter, xo-websock, xo-pywebsock, xo-tokenizer,
-#  xo-expression, xo-pyexpression, xo-reader,
+
+  xo-expression,
+  #xo-pyexpression, xo-reader,
 #  xo-jit,
 #  xo-pyjit
 
@@ -71,7 +74,8 @@ buildEnv {
             xo-ratio
             xo-unit
             xo-pyunit
-#            xo-expression
+
+            xo-expression
 #            xo-pyexpression
 #            xo-tokenizer
 #            xo-reader