diff --git a/homeassistant/components/nmap_tracker/device_tracker.py b/homeassistant/components/nmap_tracker/device_tracker.py
index 3537f01b2b8..1b528b0af7e 100644
--- a/homeassistant/components/nmap_tracker/device_tracker.py
+++ b/homeassistant/components/nmap_tracker/device_tracker.py
@@ -47,7 +47,7 @@ def _arp(ip_address):
     out, _ = arp.communicate()
     match = re.search(r'(([0-9A-Fa-f]{1,2}\:){5}[0-9A-Fa-f]{1,2})', str(out))
     if match:
-        return match.group(0)
+        return ':'.join([i.zfill(2) for i in match.group(0).split(':')])
     _LOGGER.info('No MAC address found for %s', ip_address)
     return None