diff --git a/pyheatpump/cli.py b/pyheatpump/cli.py
index 935099e..16ca754 100644
--- a/pyheatpump/cli.py
+++ b/pyheatpump/cli.py
@@ -151,7 +151,7 @@ def supervise(since):
 
     from .config import config, mac_address_init, get_last_update, set_last_update
     mac_address = config.get('heatpump','mac_address')
-    if mac_address == 'None':
+    if not re.match('^(([0-9a-f]{2}):?){6}$', mac_address, re.I):
         mac_address = mac_address_init()
 
     from .models.heatpump import Heatpump