diff --git a/admin/automerge b/admin/automerge
index 218ecb067c7..6182ad01a55 100755
--- a/admin/automerge
+++ b/admin/automerge
@@ -28,6 +28,11 @@
 ## Intended usage:
 ## Have a dedicated git directory just for this.
 ## Have a cron job that calls this script with -r -p.
+##
+## Modifying a running shell script can have unpredictable results,
+## so the paranoid will first make a copy of this script, and then run
+## it with the -d option to point to the repository directory, in case
+## a pull updates this script while it is working.
 
 die ()                 # write error to stderr and exit
 {
@@ -40,20 +45,14 @@ PD=${0%/*}
 
 [ "$PD" = "$0" ] && PD=.        # if PATH includes PWD
 
-## This should be the admin directory.
-cd $PD
-cd ../
-[ -d admin ] || die "Could not locate admin directory"
-
-[ -e .git ] || die "No .git"
-
 usage ()
 {
     cat 1>&2 <<EOF
-Usage: ${PN} [-b] [-e emacs] [-n nmin] [-p] [-r] [-t] [-- make-flags]
+Usage: ${PN} [-b] [-d dir] [-e emacs] [-n nmin] [-p] [-r] [-t] [-- mflags]
 Merge the Emacs release branch to master.
 Passes any non-option args to make (eg -- -j2).
 Options:
+-d: directory to work in (default is parent directory of this script)
 -e: Emacs executable to use for the initial merge (default $emacs)
 -n: minimum number of commits to try merging (default $nmin)
 -b: try to build after merging
@@ -74,13 +73,16 @@ test=
 push=
 quiet=
 reset=
+dir=
 
-while getopts ":hbe:n:pqrt" option ; do
+while getopts ":hbd:e:n:pqrt" option ; do
     case $option in
         (h) usage ;;
 
         (b) build=1 ;;
 
+        (d) dir=$OPTARG ;;
+
         (e) emacs=$OPTARG ;;
 
         (n) nmin=$OPTARG ;;
@@ -104,6 +106,18 @@ shift $(( --OPTIND ))
 OPTIND=1
 
 
+if [ "$dir" ]; then
+    cd "$dir" || die
+else
+    cd $PD                      # this should be the admin directory
+    cd ../
+fi
+
+[ -d admin ] || die "Could not locate admin directory"
+
+[ -e .git ] || die "No .git"
+
+
 ## Does not work 100% because a lot of Emacs batch output comes on
 ## stderr (?).
 [ "$quiet" ] && exec 1> /dev/null