diff --git a/z.sh b/z.sh
index ce50d50..75eaaf9 100755
--- a/z.sh
+++ b/z.sh
@@ -24,6 +24,9 @@ z() {
 
  local datafile="$HOME/.z"
 
+ # bail out if we don't own ~/.z (we're another user but our ENV is still set)
+ [ "$(ls -l "$datafile" | cut -d' ' -f 3)" = "$USER" ] || return
+
  # add entries
  if [ "$1" = "--add" ]; then
   shift