diff --git a/skeletons/asn_codecs_prim.h b/skeletons/asn_codecs_prim.h
index ceadf51..b928b1a 100644
--- a/skeletons/asn_codecs_prim.h
+++ b/skeletons/asn_codecs_prim.h
@@ -38,7 +38,7 @@
 	asn_TYPE_descriptor_t *type_descriptor,
 	void **struct_ptr, size_t struct_size,
 	const char *opt_mname,
-	void *buf_ptr, size_t size,
+	const void *buf_ptr, size_t size,
 	xer_primitive_body_decoder_f *prim_body_decoder
 );