diff --git a/homeassistant/components/device_tracker/nmap_tracker.py b/homeassistant/components/device_tracker/nmap_tracker.py
index 1e45444c74e..bc8e8768be0 100644
--- a/homeassistant/components/device_tracker/nmap_tracker.py
+++ b/homeassistant/components/device_tracker/nmap_tracker.py
@@ -98,7 +98,7 @@ class NmapDeviceScanner(object):
         from nmap import PortScanner, PortScannerError
         scanner = PortScanner()
 
-        options = "-F --host-timeout 5"
+        options = "-F --host-timeout 5s"
 
         if self.home_interval:
             boundary = dt_util.now() - self.home_interval