diff --git a/CHANGES.md b/CHANGES.md
index ca32a53..4e78e08 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,6 +1,9 @@
 unreleased
 ----------
 
+- Correct sexp generation for dockerfile-opam.
+  (@benmandrew #158, review by @MisterDA)
+
 - Switch to root and back to opam user when installing OCaml external
   dependencies in the ocaml stage; fixes depext installation.
   (@MisterDA #146, #157)
diff --git a/src-opam/dune b/src-opam/dune
index 8fe9763..e711792 100644
--- a/src-opam/dune
+++ b/src-opam/dune
@@ -4,6 +4,4 @@
  (synopsis "Dockerfile functions to generate opam2 base containers")
  (libraries ocaml-version dockerfile fmt sexplib astring)
  (preprocess
-  (per_module
-   ((pps ppx_sexp_conv)
-    dockerfile_distro))))
+  (pps ppx_sexp_conv)))