diff --git a/skeletons/asn_codecs_prim.h b/skeletons/asn_codecs_prim.h
index 7b75029..917c892 100644
--- a/skeletons/asn_codecs_prim.h
+++ b/skeletons/asn_codecs_prim.h
@@ -38,7 +38,7 @@
  * Specific function to decode simple primitive types.
  * Also see xer_decode_general() in xer_decoder.h
  */
-asn_dec_rval_t xer_decode_primitive(asn_codec_ctx_t *opt_codec_ctx,
+asn_dec_rval_t xer_decode_primitive(const asn_codec_ctx_t *opt_codec_ctx,
 	asn_TYPE_descriptor_t *type_descriptor,
 	void **struct_ptr, size_t struct_size,
 	const char *opt_mname,