add const
diff --git a/skeletons/ENUMERATED.c b/skeletons/ENUMERATED.c
index 4ec97c2..ffc61e3 100644
--- a/skeletons/ENUMERATED.c
+++ b/skeletons/ENUMERATED.c
@@ -54,7 +54,7 @@
 };
 
 asn_dec_rval_t
-ENUMERATED_decode_uper(asn_codec_ctx_t *opt_codec_ctx,
+ENUMERATED_decode_uper(const asn_codec_ctx_t *opt_codec_ctx,
                        asn_TYPE_descriptor_t *td,
                        const asn_per_constraints_t *constraints, void **sptr,
                        asn_per_data_t *pd) {