diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6d3cfa5d..d4846789 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -96,6 +96,7 @@ add_subdirectory(xo-simulator)
 add_subdirectory(xo-pysimulator)
 add_subdirectory(xo-process)
 add_subdirectory(xo-pyprocess)
+add_subdirectory(xo-kalmanfilter)
 #
 add_subdirectory(xo-expression)
 add_subdirectory(xo-pyexpression)
@@ -104,5 +105,4 @@ add_subdirectory(xo-reader)
 add_subdirectory(xo-jit)
 add_subdirectory(xo-pyjit)
 #
-#add_subdirectory(xo-kalmanfilter)
 #add_subdirectory(xo-pykalmanfilter)
diff --git a/default.nix b/default.nix
index 412f3c74..660f3a7b 100644
--- a/default.nix
+++ b/default.nix
@@ -69,6 +69,7 @@ let
           xo-pysimulator    = self.callPackage pkgs/xo-pysimulator.nix    {};
           xo-process        = self.callPackage pkgs/xo-process.nix        {};
           xo-pyprocess      = self.callPackage pkgs/xo-pyprocess.nix      {};
+          xo-kalmanfilter   = self.callPackage pkgs/xo-kalmanfilter.nix   {};
 #
           xo-expression     = self.callPackage pkgs/xo-expression.nix     {};
           xo-pyexpression   = self.callPackage pkgs/xo-pyexpression.nix   {};
@@ -80,8 +81,6 @@ let
                                                                             llvm = llvmPackages.llvm; };
           xo-pyjit          = self.callPackage pkgs/xo-pyjit.nix          {};
 
-#          xo-pysimulator    = self.callPackage pkgs/xo-pysimulator.nix    {};
-#          xo-kalmanfilter   = self.callPackage pkgs/xo-kalmanfilter.nix   {};
 #          xo-pykalmanfilter = self.callPackage pkgs/xo-pykalmanfilter.nix {};
 #
           xo-userenv        = self.callPackage pkgs/xo-userenv.nix        {};
diff --git a/pkgs/xo-kalmanfilter.nix b/pkgs/xo-kalmanfilter.nix
new file mode 100644
index 00000000..c350773d
--- /dev/null
+++ b/pkgs/xo-kalmanfilter.nix
@@ -0,0 +1,25 @@
+{
+  # dependencies
+  stdenv, cmake, catch2, eigen,
+
+  xo-cmake,
+  xo-statistics,
+  xo-reactor,
+} :
+
+stdenv.mkDerivation (finalattrs:
+  {
+    name = "xo-kalmanfilter";
+    version = "1.0";
+
+    src = ../xo-kalmanfilter;
+
+    cmakeFlags = ["-DCMAKE_MODULE_PATH=${xo-cmake}/share/cmake"];
+    doCheck = false;
+    nativeBuildInputs = [ cmake catch2 xo-cmake ];
+    propagatedBuildInputs = [
+      eigen
+      xo-statistics
+      xo-reactor
+    ];
+  })
diff --git a/pkgs/xo-userenv.nix b/pkgs/xo-userenv.nix
index 20425306..7728deac 100644
--- a/pkgs/xo-userenv.nix
+++ b/pkgs/xo-userenv.nix
@@ -54,7 +54,7 @@
   xo-pysimulator,
   xo-process,
   xo-pyprocess,
-  #xo-kalmanfilter,
+  xo-kalmanfilter,
   #  xo-pykalmanfilter,
 #
   xo-expression,
@@ -109,7 +109,7 @@ buildEnv {
             xo-reader
             xo-jit
             xo-pyjit
-#            xo-kalmanfilter
+            xo-kalmanfilter
 #            xo-pykalmanfilter
           ];
 }