diff --git a/src/monomorphic/dune b/src/monomorphic/dune
index c01b2478..be29afd5 100644
--- a/src/monomorphic/dune
+++ b/src/monomorphic/dune
@@ -1,5 +1,6 @@
 (library
   (name containers_monomorphic)
   (public_name containers.monomorphic)
+  (preprocess (action (run %{project_root}/src/core/cpp/cpp.exe %{input-file})))
   (modules CCMonomorphic)
   (wrapped false))