diff --git a/lib/node-libnmap.js b/lib/node-libnmap.js
index ebb03e9..ab06d18 100644
--- a/lib/node-libnmap.js
+++ b/lib/node-libnmap.js
@@ -253,7 +253,7 @@ var version = 'v0.2.11'
         , ip = new v6.Address(block)
         , ipv6 = (ip.isValid()) ? ' -6 ' : ' '
         , proto = (opts.udp) ? ' -sU' : ' '
-        , to = '--host-timeout='+opts.timeout+' ';
+        , to = '--host-timeout='+opts.timeout+'s ';
 
       return (opts.ports) ?
         opts.nmap+proto+' '+to+flags+ipv6+'-p'+opts.ports+' '+block :