diff --git a/ops/machines.nix b/ops/machines.nix
index 9a54c56c..d0e6ae3c 100644
--- a/ops/machines.nix
+++ b/ops/machines.nix
@@ -69,9 +69,14 @@ let
     ];
   })];
 
-  # mkMachine builds NixOS modules into a NixOS derivation, and injects
-  # passthru.hscloud.provision which deploys that configuration over SSH to a
-  # production machine.
+  # mkMachine builds NixOS modules into a NixOS derivation.
+  # It:
+  #  1) injects passthru.hscloud.provision which deploys that configuration
+  #     over SSH to a production machine.
+  #  2) injects 'workspace' as a nixos module argument which points to the root
+  #     of the hscloud readTree object. It will contain whatever nixpkgs
+  #     checkout this file has been invoked with, ie. will not be 'mixed in'
+  #     with the pkgs argument.
   mkMachine = pkgs: paths: pkgs.nixos ({ config, pkgs, ... }: {
     imports = paths;
 
@@ -123,6 +128,9 @@ let
       '';
     in {
       passthru.hscloud.provision = pkgs.writeScript "provision-${fqdn}" runProvision;
+
+      # TODO(q3k): this should be named hscloud, but that seems to not work. Debug and rename.
+      _module.args.workspace = hscloud;
     };
   });
 in {