diff --git a/openwisp_controller/config/base/device.py b/openwisp_controller/config/base/device.py
index f849987b..dbbf31e1 100644
--- a/openwisp_controller/config/base/device.py
+++ b/openwisp_controller/config/base/device.py
@@ -222,6 +222,7 @@ def _validate_unique_name(self):
                 )
 
     def clean(self, *args, **kwargs):
+        self.mac_address = self.mac_address.upper()
         super().clean(*args, **kwargs)
         self._validate_unique_name()
         self._validate_org_relation('group', field_error='group')