diff --git a/flake.nix b/flake.nix
index fddface..f4b91b1 100644
--- a/flake.nix
+++ b/flake.nix
@@ -10,44 +10,9 @@
       {
         packages = rec {
           performous-composer = pkgs.libsForQt5.callPackage ./performous-composer.nix {};
-          open-simh = pkgs.stdenv.mkDerivation {
-            pname = "open-simh";
-            version = "4.0.0";
-            src = pkgs.fetchFromGitHub {
-              owner = "open-simh";
-              repo = "simh";
-              rev = "d4f85d01bdf7301d5f7a2c4e51c3a84024561b26";
-              sha256 = "sha256-kjLX8JeG7nPNz7KLheQCKz8kKA1xPn0CpRg+N336r1w=";
-            };
-            postPatch = ''
-              ${pkgs.ed}/bin/ed BESM6/CMakeLists.txt <<'_EOF_'
-              /foreach (fdir \''${cand_fontdirs})/
-              i
-              string(REPLACE " " ";" extra_cand_fontdirs "$ENV{buildInputs} $ENV{nativeBuildInputs}")
-              foreach(extra_fdir IN LISTS extra_cand_fontdirs)
-                  list(APPEND cand_fontdirs ''${extra_fdir})
-              endforeach()
-              .
-              wq
-              _EOF_'';
-            buildInputs = with pkgs; [
-              libpcap
-              vde2
-              pcre
-              libedit
-              SDL2 SDL2_ttf
-              libpng
-              zlib
-              freetype
-              pkg-config
-              dejavu_fonts
-            ];
-            nativeBuildInputs = [ pkgs.cmake pkgs.ninja ];
-          };
+          open-simh = pkgs.callPackage ./open-simh.nix {};
         };
         apps = rec {
-          hello = flake-utils.lib.mkApp { drv = self.packages.${system}.hello; };
-          default = hello;
         };
       }
     );
diff --git a/open-simh.nix b/open-simh.nix
new file mode 100644
index 0000000..d796aab
--- /dev/null
+++ b/open-simh.nix
@@ -0,0 +1,48 @@
+{ stdenv, fetchFromGitHub
+, libpcap
+, vde2
+, pcre
+, libedit
+, SDL2
+, SDL2_ttf
+, libpng
+, zlib
+, freetype
+, pkg-config
+, dejavu_fonts
+, ed
+, cmake, ninja }:
+stdenv.mkDerivation {
+  pname = "open-simh";
+  version = "4.0.0";
+  src = fetchFromGitHub {
+    owner = "open-simh";
+    repo = "simh";
+    rev = "d4f85d01bdf7301d5f7a2c4e51c3a84024561b26";
+    sha256 = "sha256-kjLX8JeG7nPNz7KLheQCKz8kKA1xPn0CpRg+N336r1w=";
+  };
+  postPatch = ''
+    ${ed}/bin/ed BESM6/CMakeLists.txt <<'_EOF_'
+    /foreach (fdir \''${cand_fontdirs})/
+    i
+    string(REPLACE " " ";" extra_cand_fontdirs "$ENV{buildInputs} $ENV{nativeBuildInputs}")
+    foreach(extra_fdir IN LISTS extra_cand_fontdirs)
+        list(APPEND cand_fontdirs ''${extra_fdir})
+    endforeach()
+    .
+    wq
+    _EOF_'';
+  buildInputs = [
+    libpcap
+    vde2
+    pcre
+    libedit
+    SDL2 SDL2_ttf
+    libpng
+    zlib
+    freetype
+    pkg-config
+    dejavu_fonts
+  ];
+  nativeBuildInputs = [ cmake ninja ];
+}