diff --git a/cronjob-update-mirrors-search-db b/cronjob-update-mirrors-search-db
index 56adf9c..85c965e 100755
--- a/cronjob-update-mirrors-search-db
+++ b/cronjob-update-mirrors-search-db
@@ -6,6 +6,21 @@ SCANDIR="/data/depository"
 DBFILE="/data/sites/slackware.uk/files/repository-search/search.db"
 RUNAS_GROUP="depository"
 
+# Only allow one copy of the script to run at any time.
+# shellcheck disable=SC2154
+if [[ "$FLOCK" != "$0" ]]; then
+  # shellcheck disable=SC2093
+  exec env FLOCK="$0" flock -E 10 -e -n "$0" "$0" "$@"
+  ERR="$?"
+  if (( ERR == 10 )); then
+    # File is locked, exit now.
+    exit 0
+  elif (( ERR > 0 )); then
+    printf "%s: %s\\n" "${0##*/}" "flock execution error" >&2
+    exit 1
+  fi
+fi
+
 RAND="$$$RANDOM"
 
 if ionice -c3 nice -n 19 sg "$RUNAS_GROUP" -c "/opt/bin/updatedb -l no -o \"$DBFILE.$RAND\" -U \"$SCANDIR\" >/dev/null 2>&1"; then