diff --git a/drivers/s390/net/ism_drv.c b/drivers/s390/net/ism_drv.c
index af0d90beba63..76ba36c83e52 100644
--- a/drivers/s390/net/ism_drv.c
+++ b/drivers/s390/net/ism_drv.c
@@ -130,6 +130,7 @@ static int ism_cmd(struct ism_dev *ism, void *cmd)
 	struct ism_req_hdr *req = cmd;
 	struct ism_resp_hdr *resp = cmd;
 
+	spin_lock(&ism->cmd_lock);
 	__ism_write_cmd(ism, req + 1, sizeof(*req), req->len - sizeof(*req));
 	__ism_write_cmd(ism, req, 0, sizeof(*req));
 
@@ -143,6 +144,7 @@ static int ism_cmd(struct ism_dev *ism, void *cmd)
 	}
 	__ism_read_cmd(ism, resp + 1, sizeof(*resp), resp->len - sizeof(*resp));
 out:
+	spin_unlock(&ism->cmd_lock);
 	return resp->ret;
 }
 
@@ -630,6 +632,7 @@ static int ism_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 		return -ENOMEM;
 
 	spin_lock_init(&ism->lock);
+	spin_lock_init(&ism->cmd_lock);
 	dev_set_drvdata(&pdev->dev, ism);
 	ism->pdev = pdev;
 	ism->dev.parent = &pdev->dev;
diff --git a/include/linux/ism.h b/include/linux/ism.h
index 9a4c204df3da..04e2fc1973ce 100644
--- a/include/linux/ism.h
+++ b/include/linux/ism.h
@@ -28,6 +28,7 @@ struct ism_dmb {
 
 struct ism_dev {
 	spinlock_t lock; /* protects the ism device */
+	spinlock_t cmd_lock; /* serializes cmds */
 	struct list_head list;
 	struct pci_dev *pdev;