diff --git a/tinc-up b/tinc-up
index 238fdef..116a4c2 100755
--- a/tinc-up
+++ b/tinc-up
@@ -128,7 +128,7 @@ fi
 set_mac "$INTERFACE" "$MAC_ADDRESS"
 
 if [ -n "$SUBNET" ]; then
-  IFS=' ' read IP NETMASK <<< "SUBNET"
+  IFS=' ' read IP NETMASK <<< "$SUBNET"
   [ -z "$IP" ] && die "no ip set in SUBNET"
   [ -z "$NETMASK" ] && die "no netmask set in SUBNET"
   set_ip "$INTERFACE" "$IP" "$NETMASK"