diff --git a/drivers/scsi/qla2xxx/qla_isr.c b/drivers/scsi/qla2xxx/qla_isr.c
index 14109d86c3f6a786313bbf83d4c973e60553e33e..89f93ebd819d7590a5ece0dd689f6bd350be7393 100644
--- a/drivers/scsi/qla2xxx/qla_isr.c
+++ b/drivers/scsi/qla2xxx/qla_isr.c
@@ -272,7 +272,8 @@ qla2x00_mbx_completion(scsi_qla_host_t *vha, uint16_t mb0)
 	struct device_reg_2xxx __iomem *reg = &ha->iobase->isp;
 
 	/* Read all mbox registers? */
-	mboxes = (1 << ha->mbx_count) - 1;
+	WARN_ON_ONCE(ha->mbx_count > 32);
+	mboxes = (1ULL << ha->mbx_count) - 1;
 	if (!ha->mcp)
 		ql_dbg(ql_dbg_async, vha, 0x5001, "MBX pointer ERROR.\n");
 	else
@@ -2880,7 +2881,8 @@ qla24xx_mbx_completion(scsi_qla_host_t *vha, uint16_t mb0)
 	struct device_reg_24xx __iomem *reg = &ha->iobase->isp24;
 
 	/* Read all mbox registers? */
-	mboxes = (1 << ha->mbx_count) - 1;
+	WARN_ON_ONCE(ha->mbx_count > 32);
+	mboxes = (1ULL << ha->mbx_count) - 1;
 	if (!ha->mcp)
 		ql_dbg(ql_dbg_async, vha, 0x504e, "MBX pointer ERROR.\n");
 	else