diff --git a/bin/nd b/bin/nd
index 5e6b3a2..45cac96 100755
--- a/bin/nd
+++ b/bin/nd
@@ -2,12 +2,16 @@
 
 importas -D /bin/bash default_shell SHELL
 
-elgetopt s
+elgetopt s:
 importas -D $default_shell shell ELGETOPT_s
 elgetpositionals
 
 getcwd -E cwd
-backtick -E nixdir { find-parent -d flake.nix }
+backtick -D "" -E nixdir { find-parent -d flake.nix }
+ifelse { test $nixdir = "" } {
+  foreground { echo "flake.nix not found in parents of ${cwd}" }
+  exit 1
+}
 
 cd $nixdir
 nix develop $@ -c execlineb -c "cd ${cwd} ${shell}"