add const
diff --git a/skeletons/OCTET_STRING_oer.c b/skeletons/OCTET_STRING_oer.c
index 9e6c2aa..4ea705a 100644
--- a/skeletons/OCTET_STRING_oer.c
+++ b/skeletons/OCTET_STRING_oer.c
@@ -10,7 +10,7 @@
 #include <errno.h>
 
 asn_dec_rval_t
-OCTET_STRING_decode_oer(asn_codec_ctx_t *opt_codec_ctx,
+OCTET_STRING_decode_oer(const asn_codec_ctx_t *opt_codec_ctx,
                         asn_TYPE_descriptor_t *td,
                         const asn_oer_constraints_t *constraints, void **sptr,
                         const void *ptr, size_t size) {