diff --git a/test/blackbox-tests/test-cases/reason/cppome.re b/test/blackbox-tests/test-cases/reason/cppome.re
new file mode 100644
index 00000000..e69de29b
diff --git a/test/blackbox-tests/test-cases/reason/cppome.rei b/test/blackbox-tests/test-cases/reason/cppome.rei
new file mode 100644
index 00000000..e69de29b
diff --git a/test/blackbox-tests/test-cases/reason/jbuild b/test/blackbox-tests/test-cases/reason/jbuild
index 63d27d13..4443e620 100644
--- a/test/blackbox-tests/test-cases/reason/jbuild
+++ b/test/blackbox-tests/test-cases/reason/jbuild
@@ -5,7 +5,9 @@
 
 (library
  ((name rlib)
-  (public_name rlib)))
+  (public_name rlib)
+  (preprocess
+   (per_module ((action (run ./pp/reasononlypp.exe ${<})) (cppome))))))
 
 ;; we want to make sure that .rei files are present
 (alias
diff --git a/test/blackbox-tests/test-cases/reason/pp/jbuild b/test/blackbox-tests/test-cases/reason/pp/jbuild
new file mode 100644
index 00000000..c385afe2
--- /dev/null
+++ b/test/blackbox-tests/test-cases/reason/pp/jbuild
@@ -0,0 +1,4 @@
+(jbuild_version 1)
+
+(executable
+ ((name reasononlypp)))
diff --git a/test/blackbox-tests/test-cases/reason/pp/reasononlypp.ml b/test/blackbox-tests/test-cases/reason/pp/reasononlypp.ml
new file mode 100644
index 00000000..cb474458
--- /dev/null
+++ b/test/blackbox-tests/test-cases/reason/pp/reasononlypp.ml
@@ -0,0 +1,16 @@
+
+let () =
+  let fname = Sys.argv.(1) in
+  if Filename.check_suffix fname ".re"
+  || Filename.check_suffix fname ".rei" then (
+    let ch = open_in fname in
+    let rec loop () =
+      match input_line ch with
+      | exception End_of_file -> ()
+      | line -> print_endline line; loop () in
+    loop ();
+    close_in ch
+  ) else (
+    Format.eprintf "%s is not a reason source@.%!" fname;
+    exit 1
+  )
diff --git a/test/blackbox-tests/test-cases/reason/run.t b/test/blackbox-tests/test-cases/reason/run.t
index fafa5b56..2a6771b2 100644
--- a/test/blackbox-tests/test-cases/reason/run.t
+++ b/test/blackbox-tests/test-cases/reason/run.t
@@ -1,58 +1,19 @@
   $ $JBUILDER runtest -j1 --root .
          refmt bar.re.ml
+         refmt cppome.re.ml
+      ocamldep pp/reasononlypp.depends.ocamldep-output
          refmt hello.re.ml
          refmt pped.re.ml
         ocamlc rlib.{cmi,cmo,cmt}
+         refmt cppome.re.mli
          refmt foo.re.mli
          refmt hello.re.mli
          refmt pped.re.mli
-      ocamldep rlib.depends.ocamldep-output
+        ocamlc pp/reasononlypp.{cmi,cmo,cmt}
       ocamlopt rlib.{cmx,o}
-      ocamldep rlib.dependsi.ocamldep-output
-        ocamlc rlib__Bar.{cmi,cmti}
-        ocamlc rlib__Foo.{cmi,cmti}
-        ocamlc rlib__Hello.{cmi,cmti}
-        ocamlc rlib__Pped.{cmi,cmti}
-        ocamlc rlib__Bar.{cmo,cmt}
-      ocamlopt rlib__Bar.{cmx,o}
-        ocamlc rlib__Foo.{cmo,cmt}
-      ocamlopt rlib__Foo.{cmx,o}
-        ocamlc rlib__Hello.{cmo,cmt}
-      ocamlopt rlib__Hello.{cmx,o}
-        ocamlc rlib__Pped.{cmo,cmt}
-      ocamlopt rlib__Pped.{cmx,o}
-        ocamlc rlib.cma
-      ocamlopt rlib.{a,cmxa}
-      ocamlopt rlib.cmxs
-  lib: [
-    "_build/install/default/lib/rlib/META" {"META"}
-    "_build/install/default/lib/rlib/opam" {"opam"}
-    "_build/install/default/lib/rlib/rlib__Bar.cmi"
-    "_build/install/default/lib/rlib/rlib__Bar.cmx"
-    "_build/install/default/lib/rlib/rlib__Bar.cmt"
-    "_build/install/default/lib/rlib/rlib__Bar.cmti"
-    "_build/install/default/lib/rlib/bar.mli"
-    "_build/install/default/lib/rlib/rlib__Foo.cmi"
-    "_build/install/default/lib/rlib/rlib__Foo.cmx"
-    "_build/install/default/lib/rlib/rlib__Foo.cmt"
-    "_build/install/default/lib/rlib/rlib__Foo.cmti"
-    "_build/install/default/lib/rlib/foo.rei"
-    "_build/install/default/lib/rlib/rlib__Hello.cmi"
-    "_build/install/default/lib/rlib/rlib__Hello.cmx"
-    "_build/install/default/lib/rlib/rlib__Hello.cmt"
-    "_build/install/default/lib/rlib/rlib__Hello.cmti"
-    "_build/install/default/lib/rlib/hello.rei"
-    "_build/install/default/lib/rlib/rlib__Pped.cmi"
-    "_build/install/default/lib/rlib/rlib__Pped.cmx"
-    "_build/install/default/lib/rlib/rlib__Pped.cmt"
-    "_build/install/default/lib/rlib/rlib__Pped.cmti"
-    "_build/install/default/lib/rlib/pped.rei"
-    "_build/install/default/lib/rlib/rlib.cmi"
-    "_build/install/default/lib/rlib/rlib.cmx"
-    "_build/install/default/lib/rlib/rlib.cmt"
-    "_build/install/default/lib/rlib/rlib.ml-gen"
-    "_build/install/default/lib/rlib/rlib.cma"
-    "_build/install/default/lib/rlib/rlib.cmxa"
-    "_build/install/default/lib/rlib/rlib.a"
-    "_build/install/default/lib/rlib/rlib.cmxs"
-  ]
+      ocamlopt pp/reasononlypp.{cmx,o}
+      ocamlopt pp/reasononlypp.exe
+  reasononlypp cppome.re.pp.ml (exit 1)
+  (cd _build/default && ./pp/reasononlypp.exe cppome.re.ml) > _build/default/cppome.re.pp.ml
+  cppome.re.ml is not a reason source
+  [1]