diff --git a/homeassistant/components/device_tracker/nmap_tracker.py b/homeassistant/components/device_tracker/nmap_tracker.py
index ccd04f6cda1..e3af9ad5c44 100644
--- a/homeassistant/components/device_tracker/nmap_tracker.py
+++ b/homeassistant/components/device_tracker/nmap_tracker.py
@@ -120,7 +120,7 @@ class NmapDeviceScanner(object):
                     else:
                         mac = _arp(host.ipv4)
                     if mac:
-                        device = Device(mac, name, host.ipv4, now)
+                        device = Device(mac.upper(), name, host.ipv4, now)
                         self.last_results.append(device)
             _LOGGER.info("nmap scan successful")
             return True