diff --git a/skeletons/asn_application.c b/skeletons/asn_application.c
index 3d83478..8ce0261 100644
--- a/skeletons/asn_application.c
+++ b/skeletons/asn_application.c
@@ -131,8 +131,8 @@
 
 asn_enc_rval_t
 asn_encode(const asn_codec_ctx_t *opt_codec_ctx,
-           enum asn_transfer_syntax syntax, asn_TYPE_descriptor_t *td,
-           void *sptr, asn_app_consume_bytes_f *callback, void *callback_key) {
+           enum asn_transfer_syntax syntax, const asn_TYPE_descriptor_t *td,
+           const void *sptr, asn_app_consume_bytes_f *callback, void *callback_key) {
     struct callback_failure_catch_key cb_key;
     asn_enc_rval_t er;
 
diff --git a/skeletons/asn_application.h b/skeletons/asn_application.h
index acc91ab..3ca9f13 100644
--- a/skeletons/asn_application.h
+++ b/skeletons/asn_application.h
@@ -129,8 +129,8 @@
 asn_enc_rval_t asn_encode(
     const asn_codec_ctx_t *opt_codec_parameters, /* See asn_codecs.h */
     enum asn_transfer_syntax,
-    struct asn_TYPE_descriptor_s *type_to_encode,
-    void *structure_to_encode,
+    const struct asn_TYPE_descriptor_s *type_to_encode,
+    const void *structure_to_encode,
     asn_app_consume_bytes_f *callback, void *callback_key);