diff --git a/lib/iptables.inc b/lib/iptables.inc
index f8ccf7b..52d8f69 100644
--- a/lib/iptables.inc
+++ b/lib/iptables.inc
@@ -488,7 +488,7 @@ function enable_nat {
 			([[ ${dstaddress} != "-" ]] && [[ ${type} == "NETMAP" ]]) && dstaddress="-d ${dstaddress}"
 			# If we use a source interface, the rule can't go in a POSTROUTING table like what NAT is, so we punt it to PREROUTING
 			# or it won't work.  Plus we remove the destination interface too.
-			([[ ${srcinterface} != "-" ]] && [[ ${type} == "NETMAP" ]]) && NAT="PREROUTING" && dstinterface="-"
+			([[ ${srcinterface} != "-" ]] && [[ ${type} == "NETMAP" ]]) && NAT="PREROUTING" && dstinterface="-" && srcinterface="-i ${srcinterface}"
 			([[ ${custom} == "" ]] && [[ ${type} == "NETMAP" ]]) && \
 					${display} RED "nat.conf: Error - NETMAP rule can not have empty custom address: ${DEFAULT_COLOR}${type} ${srcinterface} ${srcaddress} ${dstinterface} ${dstaddress} ${custom}" \
 					&& continue