diff --git a/mm/percpu.c b/mm/percpu.c
index 7e2aa0305c27..7e06a1e58720 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2125,7 +2125,7 @@ struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups,
 	void *ptr;
 	int unit;
 
-	base_size = ALIGN(sizeof(*ai) + nr_groups * sizeof(ai->groups[0]),
+	base_size = ALIGN(struct_size(ai, groups, nr_groups),
 			  __alignof__(ai->groups[0].cpu_map[0]));
 	ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]);