diff --git a/scripts/bind-add-ng.sh b/scripts/bind-add-ng.sh
index 001fc42..8b25d85 100755
--- a/scripts/bind-add-ng.sh
+++ b/scripts/bind-add-ng.sh
@@ -73,9 +73,9 @@ inc_and_reload () {
     zonefile="$BINDROOT/db.$domain"
 
     # Set the date for serial (only if greater than actual serial)
-    serial=$(grep -P '^[ \t]*[0-9]{10}[ \t]*; serial' $zonefile | sed "s/^[ \t]*\([0-9]\{10\}\)[ \t]*; serial/\1/")
+    serial=$(grep -P '^[ \t]*[0-9]{10}[ \t]*; serial' $zonefile | sed -r "s/^[ \t]*([0-9]{10})[ \t]*; serial/\1/")
     if [ `date "+%Y%m%d%H"` -gt $serial ]; then serial=$(date "+%Y%m%d%H"); else serial=$(( $serial + 1 )); fi
-    sed -i "s/^\([ \t]*\)[0-9]\{10\}\([ \t]*; serial\)/\1$serial\2/" \
+    sed -ri "s/^([ \t]*)[0-9]{10}([ \t]*; serial)/\1$serial\2/" \
       $zonefile
     if stderr=$(named-checkzone $domain $zonefile 2>&1); then
         rndc reload