diff --git a/debian/check-mk-multisite.postinst b/debian/check-mk-multisite.postinst
--- /dev/null
@@ -0,0 +1,32 @@
+#!/bin/bash
+
+set -e
+
+. /usr/share/debconf/confmodule
+
+setperm() {
+ local user="$1"
+ local group="$2"
+ local mode="$3"
+ local file="$4"
+ shift 4
+ # only do something when no setting exists
+ if ! dpkg-statoverride --list "$file" >/dev/null 2>&1; then
+ chown "$user":"$group" "$file"
+ chmod "$mode" "$file"
+ fi
+}
+
+case "$1" in
+ configure)
+ # explicitly set permissions on some files
+ setperm www-data www-data 770 /var/lib/check_mk/web
+ ;;
+ abort-upgrade|abort-remove|abort-deconfigure)
+ ;;
+ *)
+ echo "postinst called with unknown argument \$1'" >&2
+ exit 1
+ ;;
+esac
+