diff --git a/hack/tfw.sh b/hack/tfw.sh
index b22e3f4..d80b737 100755
--- a/hack/tfw.sh
+++ b/hack/tfw.sh
@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-set -e
+set -eu
 set -o pipefail
 set -o errtrace
 shopt -s expand_aliases