diff --git a/images/cachix/default.nix b/images/cachix/default.nix
new file mode 100644
index 0000000..bbc7f12
--- /dev/null
+++ b/images/cachix/default.nix
@@ -0,0 +1,6 @@
+{ docker-nixpkgs
+, cachix
+}:
+docker-nixpkgs.nix.override {
+  extraContents = [ cachix ];
+}
diff --git a/images/nix/default.nix b/images/nix/default.nix
index b5bd52a..635278f 100644
--- a/images/nix/default.nix
+++ b/images/nix/default.nix
@@ -9,6 +9,7 @@
 , iana-etc
 , nix
 , xz
+, extraContents ? []
 }:
 let
   image = dockerTools.buildImageWithNixDb {
@@ -30,7 +31,7 @@ let
 
       # for haskell binaries
       iana-etc
-    ];
+    ] ++ extraContents;
 
     extraCommands = ''
       # for /usr/bin/env