diff --git a/default.nix b/default.nix
index 7f48895..7b66620 100644
--- a/default.nix
+++ b/default.nix
@@ -1,6 +1,6 @@
-args@{ pkgs ? import ./nix args, system ? null, ... }:
-
+{ pkgs ? import ./nix {}
+, haskellPackages ? pkgs.haskellPackages
+}:
 {
-  inherit (pkgs) arion tests;
-  doc = pkgs.recurseIntoAttrs (import ./doc { inherit pkgs; });
+  arion = import ./nix/arion.nix { inherit pkgs haskellPackages; };
 }
diff --git a/nix/arion.nix b/nix/arion.nix
new file mode 100644
index 0000000..4b76fc1
--- /dev/null
+++ b/nix/arion.nix
@@ -0,0 +1,42 @@
+{ pkgs ? import ./. {}
+, lib ? pkgs.lib
+, haskellPackages ? pkgs.haskellPackages
+, arion-compose ? import ./haskell-arion-compose.nix { inherit pkgs haskellPackages; }
+}:
+
+let
+  inherit (pkgs.haskell.lib) justStaticExecutables overrideCabal;
+
+  srcDir = ../src;
+  eval = import (srcDir + "/nix/eval-composition.nix");
+  build = args@{...}:
+    let composition = eval args;
+    in composition.config.build.dockerComposeYaml;
+
+in
+  justStaticExecutables (overrideCabal arion-compose (o: {
+    buildTools = o.buildTools ++ [pkgs.makeWrapper];
+    passthru = o.passthru // {
+      inherit eval build;
+    };
+    pname = "arion"; # Cover up the needlessly long Haskell package name
+
+    # PYTHONPATH
+    #
+    # We close off the python module search path!
+    #
+    # Accepting directories from the environment into the search path
+    # tends to break things. Docker Compose does not have a plugin
+    # system as far as I can tell, so I don't expect this to break a
+    # feature, but rather to make the program more robustly self-
+    # contained.
+
+    postInstall = ''${o.postInstall or ""}
+      mkdir -p $out/libexec
+      mv $out/bin/arion $out/libexec
+      makeWrapper $out/libexec/arion $out/bin/arion \
+        --unset PYTHONPATH \
+        --prefix PATH : ${lib.makeBinPath [ pkgs.docker-compose ]} \
+        ;
+    '';
+  }))
diff --git a/nix/ci.nix b/nix/ci.nix
new file mode 100644
index 0000000..91f1a0f
--- /dev/null
+++ b/nix/ci.nix
@@ -0,0 +1,6 @@
+args@{ pkgs ? import ./default.nix args, system ? null, ... }:
+
+{
+  inherit (pkgs) arion tests;
+  doc = pkgs.recurseIntoAttrs (import ../doc { inherit pkgs; });
+}
diff --git a/nix/haskell-arion-compose.nix b/nix/haskell-arion-compose.nix
new file mode 100644
index 0000000..239d476
--- /dev/null
+++ b/nix/haskell-arion-compose.nix
@@ -0,0 +1,14 @@
+
+# NOTE: This file produces a haskell library, not the arion package!
+
+{ pkgs ? import ./default.nix {}, haskellPackages ? pkgs.haskellPackages }:
+let
+  inherit (pkgs.haskell.lib) overrideCabal addBuildTools;
+in
+  overrideCabal (addBuildTools (haskellPackages.callCabal2nix "arion-compose" ./.. {}) [pkgs.nix]) (o: o // {
+    preCheck = ''
+      export NIX_LOG_DIR=$TMPDIR
+      export NIX_STATE_DIR=$TMPDIR
+      export NIX_PATH=nixpkgs=${pkgs.path}
+    '';
+  })
\ No newline at end of file
diff --git a/nix/haskell-overlay.nix b/nix/haskell-overlay.nix
index 74e43c4..c2d82cb 100644
--- a/nix/haskell-overlay.nix
+++ b/nix/haskell-overlay.nix
@@ -1,13 +1,4 @@
 self: super: hself: hsuper:
-let
-  inherit (self.haskell.lib) addBuildTools overrideCabal;
-in
 {
-  arion-compose = overrideCabal (addBuildTools (hself.callCabal2nix "arion-compose" ./.. {}) [self.nix]) (o: o // {
-    preCheck = ''
-      export NIX_LOG_DIR=$TMPDIR
-      export NIX_STATE_DIR=$TMPDIR
-      export NIX_PATH=nixpkgs=${self.path}
-    '';
-  });
+  arion-compose = import ./haskell-arion-compose.nix { pkgs = self; haskellPackages = hself; };
 }
\ No newline at end of file
diff --git a/nix/overlay.nix b/nix/overlay.nix
index 6a41e14..8b5490c 100644
--- a/nix/overlay.nix
+++ b/nix/overlay.nix
@@ -3,42 +3,10 @@ let
   inherit (self.arion-project) haskellPkgs;
   inherit (super) lib;
 
-  srcDir = ../src; # TODO gitignoreSource + whitelist nix and arion-image
-  eval = import (srcDir + "/nix/eval-composition.nix");
-  build = args@{...}:
-    let composition = eval args;
-    in composition.config.build.dockerComposeYaml;
-  hlib = super.haskell.lib;
 in
 {
 
-  arion-v0 = super.callPackage ../arion.nix {};
-  arion = hlib.justStaticExecutables (hlib.overrideCabal haskellPkgs.arion-compose (o: {
-      buildTools = o.buildTools ++ [super.makeWrapper];
-      passthru = o.passthru // {
-        inherit eval build;
-      };
-      pname = "arion"; # Cover up the needlessly long Haskell package name
-
-      # PYTHONPATH
-      #
-      # We close off the python module search path!
-      #
-      # Accepting directories from the environment into the search path
-      # tends to break things. Docker Compose does not have a plugin
-      # system as far as I can tell, so I don't expect this to break a
-      # feature, but rather to make the program more robustly self-
-      # contained.
-
-      postInstall = ''${o.postInstall or ""}
-        mkdir -p $out/libexec
-        mv $out/bin/arion $out/libexec
-        makeWrapper $out/libexec/arion $out/bin/arion \
-          --unset PYTHONPATH \
-          --prefix PATH : ${lib.makeBinPath [ self.docker-compose ]} \
-          ;
-      '';
-    }));
+  arion = import ./arion.nix { pkgs = self; };
   tests = super.callPackage ../tests {};
   doc = super.callPackage ../doc {};
 
@@ -50,6 +18,7 @@ in
         haskellPkgs.cabal-install
         haskellPkgs.ghcid
         super.docker-compose
+        (import ~/h/ghcide-nix {}).ghcide-ghc864
       ];
     };
   };