diff --git a/.docker/hierarchic.Dockerfile b/.docker/hierarchic.Dockerfile
index b2edb1d9..b76adebf 100644
--- a/.docker/hierarchic.Dockerfile
+++ b/.docker/hierarchic.Dockerfile
@@ -6,6 +6,9 @@ FROM fstar:local-branch-$FSTAR_BRANCH
 ADD --chown=opam:opam ./ $HOME/karamel/
 WORKDIR $HOME/karamel
 
+# Let OPAM do its thing
+ENV OPAMYES=1
+
 # CI dependencies: node.js, ctypes-foreign
 RUN opam depext ctypes-foreign uucp
 RUN opam install ctypes-foreign uucp
diff --git a/karamel.opam b/karamel.opam
index 375a72b8..eb26f6a4 100644
--- a/karamel.opam
+++ b/karamel.opam
@@ -22,6 +22,8 @@ depends: [
   "ppx_deriving"
   "ppx_deriving_yojson"
   "fstar"
+  "ctypes"
+  "ctypes-foreign"
   "uucp"
 ]
 depexts: ["coreutils"] {os = "macos" & os-distribution = "homebrew"}