diff --git a/src/gen_rules.ml b/src/gen_rules.ml
index 8ccb6aa6..3584172b 100644
--- a/src/gen_rules.ml
+++ b/src/gen_rules.ml
@@ -1008,12 +1008,9 @@ module Gen(P : Params) = struct
               ; if_ (native && Module.has_impl m)
                   [ Module.cm_file_unsafe m ~obj_dir Cmx ]
               ; List.filter_map Ml_kind.all ~f:(Module.cmt_file m ~obj_dir)
-              ; [ let file =
-                    match m.intf with
-                    | Some f -> f
-                    | None -> Option.value_exn m.impl
-                  in
-                  Path.relative dir file.name ]
+              ; List.filter_map [m.intf;m.impl] ~f:(function
+                  | None -> None
+                  | Some f -> Some (Path.relative dir f.name))
               ])
         ; if_ byte [ lib_archive ~dir lib ~ext:".cma" ]
         ; if_ (Library.has_stubs lib) [ stubs_archive ~dir lib ]
diff --git a/test/blackbox-tests/test-cases/gen-opam-install-file/run.t b/test/blackbox-tests/test-cases/gen-opam-install-file/run.t
index c86360f3..6ee52ff4 100644
--- a/test/blackbox-tests/test-cases/gen-opam-install-file/run.t
+++ b/test/blackbox-tests/test-cases/gen-opam-install-file/run.t
@@ -22,6 +22,7 @@
     "_build/install/default/lib/foo/foo.cmt"
     "_build/install/default/lib/foo/foo.cmti"
     "_build/install/default/lib/foo/foo.mli"
+    "_build/install/default/lib/foo/foo.ml"
     "_build/install/default/lib/foo/foo.cma"
     "_build/install/default/lib/foo/foo.cmxa"
     "_build/install/default/lib/foo/foo.a"