diff --git a/attach.c b/attach.c
index 99e101d..059b510 100644
--- a/attach.c
+++ b/attach.c
@@ -237,12 +237,16 @@ attach_main(int noerror)
 		/* stdin activity */
 		if (n > 0 && FD_ISSET(0, &readfds))
 		{
+			ssize_t len;
+
 			pkt.type = MSG_PUSH;
 			memset(pkt.u.buf, 0, sizeof(pkt.u.buf));
-			pkt.len = read(0, pkt.u.buf, sizeof(pkt.u.buf));
+			len = read(0, pkt.u.buf, sizeof(pkt.u.buf));
 
-			if (pkt.len <= 0)
+			if (len <= 0)
 				exit(1);
+
+			pkt.len = len;
 			process_kbd(s, &pkt);
 			n--;
 		}
diff --git a/master.c b/master.c
index e65d269..e0351bd 100644
--- a/master.c
+++ b/master.c
@@ -351,7 +351,10 @@ client_activity(struct client *p)
 
 	/* Push out data to the program. */
 	if (pkt.type == MSG_PUSH)
-		write(the_pty.fd, pkt.u.buf, pkt.len);
+	{
+		if (pkt.len <= sizeof(pkt.u.buf))
+			write(the_pty.fd, pkt.u.buf, pkt.len);
+	}
 
 	/* Attach or detach from the program. */
 	else if (pkt.type == MSG_ATTACH)