diff --git a/drivers/infiniband/hw/qib/qib_user_sdma.c b/drivers/infiniband/hw/qib/qib_user_sdma.c
index 3e0677c51276..deef6ffc3f0d 100644
--- a/drivers/infiniband/hw/qib/qib_user_sdma.c
+++ b/drivers/infiniband/hw/qib/qib_user_sdma.c
@@ -41,6 +41,7 @@
 #include <linux/rbtree.h>
 #include <linux/spinlock.h>
 #include <linux/delay.h>
+#include <linux/overflow.h>
 
 #include "qib.h"
 #include "qib_user_sdma.h"
@@ -908,10 +909,11 @@ static int qib_user_sdma_queue_pkts(const struct qib_devdata *dd,
 		}
 
 		if (frag_size) {
-			int pktsize, tidsmsize, n;
+			int tidsmsize, n;
+			size_t pktsize;
 
 			n = npages*((2*PAGE_SIZE/frag_size)+1);
-			pktsize = sizeof(*pkt) + sizeof(pkt->addr[0])*n;
+			pktsize = struct_size(pkt, addr, n);
 
 			/*
 			 * Determine if this is tid-sdma or just sdma.