diff --git a/org/channel-tui-main.org b/org/channel-tui-main.org
index 8baec68..8d624d1 100644
--- a/org/channel-tui-main.org
+++ b/org/channel-tui-main.org
@@ -917,6 +917,9 @@ Event handlers + daemon I/O + main loop.
                                               :stderr nil))
                (tty-in (uiop:process-info-output cat-proc)))
           (add-msg :system (format nil "* cat pid=~a *" (uiop:process-info-pid cat-proc)))
+          ;; Guard against nil w/h from backend-size
+          (setq w (or (and (numberp w) (> w 0) w) 80)
+                h (or (and (numberp h) (> h 0) h) 24))
           ;; Log backend info and terminal dimensions
           (let ((backend-type (if (typep be 'cl-tty.backend:modern-backend)
                                   "modern" "simple")))