diff --git a/tools/kwboot.c b/tools/kwboot.c
index 7e1be29623..695d433b96 100644
--- a/tools/kwboot.c
+++ b/tools/kwboot.c
@@ -1151,6 +1151,7 @@ kwboot_terminal(int tty)
 		fd_set rfds;
 		int nfds = 0;
 
+		FD_ZERO(&rfds);
 		FD_SET(tty, &rfds);
 		nfds = nfds < tty ? tty : nfds;