diff --git a/skeletons/ber_decoder.h b/skeletons/ber_decoder.h
index 2049428..e9907bd 100644
--- a/skeletons/ber_decoder.h
+++ b/skeletons/ber_decoder.h
@@ -22,7 +22,7 @@
  * NOTE: Use the der_encode() function (der_encoder.h) to produce encoding
  * which is compliant with ber_decode().
  */
-asn_dec_rval_t ber_decode(struct asn_codec_ctx_s *opt_codec_ctx,
+asn_dec_rval_t ber_decode(const struct asn_codec_ctx_s *opt_codec_ctx,
 	struct asn_TYPE_descriptor_s *type_descriptor,
 	void **struct_ptr,	/* Pointer to a target structure's pointer */
 	const void *buffer,	/* Data to be decoded */
@@ -33,7 +33,7 @@
  * Type of generic function which decodes the byte stream into the structure.
  */
 typedef asn_dec_rval_t (ber_type_decoder_f)(
-		struct asn_codec_ctx_s *opt_codec_ctx,
+		const struct asn_codec_ctx_s *opt_codec_ctx,
 		struct asn_TYPE_descriptor_s *type_descriptor,
 		void **struct_ptr, const void *buf_ptr, size_t size,
 		int tag_mode);
@@ -50,7 +50,7 @@
  * head->last_tag_form is non-zero.
  */
 asn_dec_rval_t ber_check_tags(
-		struct asn_codec_ctx_s *opt_codec_ctx,	/* codec options */
+		const struct asn_codec_ctx_s *opt_codec_ctx,	/* codec options */
 		struct asn_TYPE_descriptor_s *type_descriptor,
 		asn_struct_ctx_t *opt_ctx,	/* saved decoding context */
 		const void *ptr, size_t size,