diff --git a/net/system.sh b/net/system.sh
index 2cbab9c7..aa654a10 100644
--- a/net/system.sh
+++ b/net/system.sh
@@ -58,8 +58,8 @@ _system_ntp()
 	local servers= buffer= x=
 
 	eval servers=\$ntp_servers_${IFVAR}
-	[ -z ${servers} ] && servers=${ntp_servers}
-	[ -z ${servers} ] && return 0
+	[ -z "${servers}" ] && servers=${ntp_servers}
+	[ -z "${servers}" ] && return 0
 
 	buffer="# Generated by net-scripts for interface ${IFACE}\n"
 	buffer="${buffer}restrict default noquery notrust nomodify\n"