diff --git a/plugin/bignums_syntax.ml b/plugin/bignums_syntax.ml
index 1f668aa..e47e264 100644
--- a/plugin/bignums_syntax.ml
+++ b/plugin/bignums_syntax.ml
@@ -128,7 +128,7 @@ let bigN_of_pos_bigint ?loc n =
   DAst.make ?loc @@ GApp (ref_constructor, args)
 
 let bigN_error_negative ?loc =
-  CErrors.user_err ?loc ~hdr:"interp_bigN" (Pp.str "bigN are only non-negative numbers.")
+  CErrors.user_err ?loc Pp.(str "bigN are only non-negative numbers.")
 
 let interp_bigN ?loc n =
   if Z.(leq zero n) then