diff --git a/hm/scripts/overpdf b/hm/scripts/overpdf
index 32cbcd6..310d8aa 100755
--- a/hm/scripts/overpdf
+++ b/hm/scripts/overpdf
@@ -1,7 +1,9 @@
 #!/usr/bin/env nix-shell
-#! nix-shell -i bash --pure
+#! nix-shell -i bash
 #! nix-shell -p bash pdftk inkscape gnused coreutils file
 
+set -euxo pipefail
+
 # Utility to write over a PDF file pages
 
 # TODO Inkscape vodoo: Put the original in its own layer and skip when merging