diff --git a/drivers/usb/emul/sandbox_flash.c b/drivers/usb/emul/sandbox_flash.c
index cc80f67..01b2b41 100644
--- a/drivers/usb/emul/sandbox_flash.c
+++ b/drivers/usb/emul/sandbox_flash.c
@@ -228,9 +228,9 @@
 			ulong transfer_len)
 {
 	debug("%s: lba=%lx, transfer_len=%lx\n", __func__, lba, transfer_len);
+	priv->read_len = transfer_len;
 	if (priv->fd != -1) {
 		os_lseek(priv->fd, lba * SANDBOX_FLASH_BLOCK_LEN, OS_SEEK_SET);
-		priv->read_len = transfer_len;
 		setup_response(priv, priv->buff,
 			       transfer_len * SANDBOX_FLASH_BLOCK_LEN);
 	} else {
@@ -336,6 +336,9 @@
 			if (priv->read_len) {
 				ulong bytes_read;
 
+				if (priv->fd == -1)
+					return -EIO;
+
 				bytes_read = os_read(priv->fd, buff, len);
 				if (bytes_read != len)
 					return -EIO;