added consts

diff --git a/skeletons/constr_CHOICE.c b/skeletons/constr_CHOICE.c
index 2cfac3b..e6d08ba 100644
--- a/skeletons/constr_CHOICE.c
+++ b/skeletons/constr_CHOICE.c
@@ -456,12 +456,14 @@
 
 	if(present > 0 || present <= specs->elements_count) {
 		asn1_CHOICE_element_t *elm = &specs->elements[present-1];
-		void *memb_ptr;
+		const void *memb_ptr;
 
 		if(elm->optional) {
-			memb_ptr = *(void **)((char *)ptr + elm->memb_offset);
+			memb_ptr = *(const void * const *)
+					((const char *)ptr + elm->memb_offset);
 		} else {
-			memb_ptr = (void *)((char *)ptr + elm->memb_offset);
+			memb_ptr = (const void *)
+					((const char *)ptr + elm->memb_offset);
 		}
 
 		return asn1_TYPE_outmost_tag(elm->type, memb_ptr,