diff --git a/src/cbor/dune b/src/cbor/dune
index 0810df8b..eda56ef1 100644
--- a/src/cbor/dune
+++ b/src/cbor/dune
@@ -1,4 +1,5 @@
 (library
   (name containers_cbor)
   (libraries containers)
+  (preprocess (action (run %{project_root}/src/core/cpp/cpp.exe %{input-file})))
   (public_name containers.cbor))