diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d8bdbe1..e3565ec 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4255,10 +4255,9 @@ static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
 	new->size = size;
 
 	/* Copy thresholds (if any) to new array */
-	if (thresholds->primary) {
-		memcpy(new->entries, thresholds->primary->entries, (size - 1) *
-				sizeof(struct mem_cgroup_threshold));
-	}
+	if (thresholds->primary)
+		memcpy(new->entries, thresholds->primary->entries,
+		       flex_array_size(new, entries, size - 1));
 
 	/* Add new threshold */
 	new->entries[size - 1].eventfd = eventfd;