diff --git a/tmux.h b/tmux.h
index 0aa2b854..52180809 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1458,6 +1458,7 @@ void	tty_putc(struct tty *, u_char);
 void	tty_pututf8(struct tty *, const struct grid_utf8 *);
 void	tty_init(struct tty *, int, char *);
 int	tty_resize(struct tty *);
+int	tty_set_size(struct tty *tty, u_int sx, u_int sy);
 void	tty_start_tty(struct tty *);
 void	tty_stop_tty(struct tty *);
 void	tty_set_title(struct tty *, const char *);
diff --git a/tty.c b/tty.c
index 6e3e2cf2..6b0e503d 100644
--- a/tty.c
+++ b/tty.c
@@ -93,10 +93,8 @@ tty_resize(struct tty *tty)
 		sx = 80;
 		sy = 24;
 	}
-	if (sx == tty->sx && sy == tty->sy)
+	if (!tty_set_size(tty, sx, sy))
 		return (0);
-	tty->sx = sx;
-	tty->sy = sy;
 
 	tty->cx = UINT_MAX;
 	tty->cy = UINT_MAX;
@@ -116,6 +114,15 @@ tty_resize(struct tty *tty)
 	return (1);
 }
 
+int
+tty_set_size(struct tty *tty, u_int sx, u_int sy) {
+	if (sx == tty->sx && sy == tty->sy)
+		return (0);
+	tty->sx = sx;
+	tty->sy = sy;
+	return (1);
+}
+
 int
 tty_open(struct tty *tty, const char *overrides, char **cause)
 {