diff --git a/Shorewall-perl/prog.header b/Shorewall-perl/prog.header
index f3fc09f7e..569e1ec45 100644
--- a/Shorewall-perl/prog.header
+++ b/Shorewall-perl/prog.header
@@ -912,11 +912,17 @@ find_mac() # $1 = IP address, $2 = interface
 {
     qt ping -nc 1 -t 2 -I $2 $1
 
-    local result=$(arp -na |  awk "/[(]$1[)].* on $2$/ {print \$4}")
+    local result=$(arp -na |  awk "/[(]$1[)].* $2$/ {print \$4}")
 
-    [ -n "$result" -a "$result" != "<incomplete>" ] || fatal_error "Cannot determine the MAC address of $1 through $2"
+    case $result in
+	\<*\>)
+	    ;;
+	*)
+	    [ -n "$result" ] && echo $result && return
+	    ;;
+    esac
 
-    echo $result
+    fatal_error "Cannot determine the MAC address of $1 through $2"
 }
 
 ################################################################################