diff --git a/shell/default.nix b/shell/default.nix
index 56ae06ea9bc5ccb6aa9ad661dd9161f494865c2d..82d9f15784076ee0c2f56b0d1af9ada82ec7d46e 100644
--- a/shell/default.nix
+++ b/shell/default.nix
@@ -13,6 +13,8 @@ let
     containers
     dhall
     http-conduit
+    horizon-gen-nix
+    horizon-spec
     lens
     lens-aeson
     path