diff --git a/core/dive.c b/core/dive.c
index e96036611..a4a47ab90 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -2614,7 +2614,6 @@ struct dive *merge_dives(const struct dive *a, const struct dive *b, int offset,
 	MERGE_MAX(res, a, b, rating);
 	MERGE_TXT(res, a, b, suit, ", ");
 	MERGE_MAX(res, a, b, number);
-	MERGE_NONZERO(res, a, b, cns);
 	MERGE_NONZERO(res, a, b, visibility);
 	copy_pictures(a->pictures.nr ? &a->pictures : &b->pictures, &res->pictures);
 	taglist_merge(&res->tag_list, a->tag_list, b->tag_list);
@@ -2631,6 +2630,9 @@ struct dive *merge_dives(const struct dive *a, const struct dive *b, int offset,
 	else
 		join_dive_computers(res, &res->dc, &a->dc, &b->dc, cylinders_map_a, cylinders_map_b, 0);
 
+	/* The CNS values will be recalculated from the sample in fixup_dive() */
+	res->cns = res->maxcns = 0;
+
 	/* we take the first dive site, unless it's empty */
 	*site = a->dive_site && !dive_site_is_empty(a->dive_site) ? a->dive_site : b->dive_site;
 	fixup_dive(res);