diff --git a/libasn1fix/asn1fix_class.h b/libasn1fix/asn1fix_class.h
index 2120bc8..b0c143b 100644
--- a/libasn1fix/asn1fix_class.h
+++ b/libasn1fix/asn1fix_class.h
@@ -4,6 +4,6 @@
 /*
  * Fetch the element from the class-related stuff (thing) by its reference.
  */
-asn1p_expr_t *asn1f_class_access(arg_t *, asn1p_module_t *mod, asn1p_expr_t *rhs_pspecs, asn1p_ref_t *);
+asn1p_expr_t *asn1f_class_access(arg_t *, asn1p_module_t *mod, asn1p_expr_t *rhs_pspecs, const asn1p_ref_t *);
 
 #endif	/* ASN1FIX_CLASS_H */