diff --git a/horizon.dhall b/horizon.dhall
index a145fe76e90ffe02fe8fd94e4346e729cb7c599d..f27faa86b7486137e957d43771cf112ceb156fcc 100644
--- a/horizon.dhall
+++ b/horizon.dhall
@@ -378,6 +378,7 @@ in  H.HorizonExport.MakePackageSet
           , H.callHackage "hledger" "1.27.1"
           , H.callHackage "hlint" "3.5"
           , H.callHackage "hopenssl" "2.2.4"
+          , H.callHackage "horizon-spec" "0.4.1"
           , H.callHackage "hosc" "0.19.1"
           , H.callHackage "hostname" "1.0"
           , H.callHackage "hourglass" "0.2.12"
diff --git a/initial-packages.nix b/initial-packages.nix
index 9238edd0c30d16b2cb0ac6cb14a2cdf2133ccd7e..34a607ede042a77bee5729152c72ca66c7b13c70 100644
--- a/initial-packages.nix
+++ b/initial-packages.nix
@@ -587,6 +587,8 @@ self: with pkgs.haskell.lib; {
 
   horizon-gen-nix = self.callPackage (./pkgs/horizon-gen-nix.nix) { };
 
+  horizon-spec = self.callPackage (./pkgs/horizon-spec.nix) { };
+
   hosc = self.callPackage (./pkgs/hosc.nix) { };
 
   hostname = self.callPackage (./pkgs/hostname.nix) { };
diff --git a/pkgs/horizon-spec.nix b/pkgs/horizon-spec.nix
new file mode 100644
index 0000000000000000000000000000000000000000..09f409cc3c32d6acc9d868f49726ea2488681225
--- /dev/null
+++ b/pkgs/horizon-spec.nix
@@ -0,0 +1,45 @@
+{ mkDerivation
+, base
+, containers
+, dhall
+, lib
+, path
+, path-dhall-instance
+, prettyprinter
+, sydtest
+, text
+}:
+mkDerivation {
+  pname = "horizon-spec";
+  version = "0.4.1";
+  sha256 = "4cf5ba59489bca20edf7c82c69ce565c69c900c863bf3f335c887f6784e929f7";
+  isLibrary = true;
+  isExecutable = true;
+  enableSeparateDataOutput = false;
+  libraryHaskellDepends = [
+    base
+    containers
+    dhall
+    path
+    path-dhall-instance
+    text
+  ];
+  executableHaskellDepends = [
+    base
+    dhall
+    prettyprinter
+    sydtest
+    text
+  ];
+  enableLibraryProfiling = true;
+  enableExecutableProfiling = true;
+  doHaddock = false;
+  jailbreak = true;
+  doCheck = false;
+  doBenchmark = false;
+  hyperlinkSource = false;
+  homepage = "https://horizon-haskell.net";
+  description = "Horizon Stable Package Set Type Definitions";
+  license = lib.licenses.mit;
+  broken = false;
+}