diff --git a/src/plugins/e-acsl/main.ml b/src/plugins/e-acsl/main.ml
index 07328232f11d5bcb15f346e1e587e88caa2aa8b7..e1d7ac2aa2dcf8f8f236d26d2953d0307c320593 100644
--- a/src/plugins/e-acsl/main.ml
+++ b/src/plugins/e-acsl/main.ml
@@ -64,7 +64,7 @@ let unmemoized_extend_ast () =
     let register s =
       File.pre_register
         (File.NeedCPP
-           (Datatype.Filepath.of_string s,
+           (s,
             ppc
             ^ Format.asprintf " -I%s" share,
             ppk))