diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
index c5e6545f6fcf..8e8a8bf518b6 100644
--- a/arch/um/drivers/ubd_user.c
+++ b/arch/um/drivers/ubd_user.c
@@ -41,7 +41,7 @@ int start_io_thread(struct os_helper_thread **td_out, int *fd_out)
 	*fd_out = fds[1];
 
 	err = os_set_fd_block(*fd_out, 0);
-	err = os_set_fd_block(kernel_fd, 0);
+	err |= os_set_fd_block(kernel_fd, 0);
 	if (err) {
 		printk("start_io_thread - failed to set nonblocking I/O.\n");
 		goto out_close;