add const
diff --git a/skeletons/UniversalString.c b/skeletons/UniversalString.c
index 88d54c6..453c6a8 100644
--- a/skeletons/UniversalString.c
+++ b/skeletons/UniversalString.c
@@ -146,7 +146,7 @@
 }
 
 asn_dec_rval_t
-UniversalString_decode_xer(asn_codec_ctx_t *opt_codec_ctx,
+UniversalString_decode_xer(const asn_codec_ctx_t *opt_codec_ctx,
 	asn_TYPE_descriptor_t *td, void **sptr,
 		const char *opt_mname, const void *buf_ptr, size_t size) {
 	asn_dec_rval_t rc;