diff --git a/skills/agentic-end-to-end-testing/driving-cli-tui.md b/skills/agentic-end-to-end-testing/driving-cli-tui.md
index 8a5ea48a..cd6f1319 100644
--- a/skills/agentic-end-to-end-testing/driving-cli-tui.md
+++ b/skills/agentic-end-to-end-testing/driving-cli-tui.md
@@ -19,7 +19,10 @@ cleanup() {
 }
 trap cleanup EXIT
 
-tmux new-session -d -s "$session" -x 200 -y 50 "<cmd> 2>\"$stderr_log\""
+if ! tmux new-session -d -s "$session" -x 200 -y 50 "<cmd> 2>\"$stderr_log\""; then
+  echo "failed to create tmux session: $session" >&2
+  exit 1
+fi
 session_owned=1
 tmux send-keys -t "$session" -l "literal text"   # -l = no key-name parsing (paths, slashes)
 tmux send-keys -t "$session" Enter