diff --git a/netbox/extras/models/customfields.py b/netbox/extras/models/customfields.py
index a433a3f81..6f6825110 100644
--- a/netbox/extras/models/customfields.py
+++ b/netbox/extras/models/customfields.py
@@ -153,7 +153,7 @@ class CustomField(BigIDModel):
                 self.validate(default_value)
             except ValidationError as err:
                 raise ValidationError({
-                    'default': f'Invalid default value "{self.default}": {err.message}'
+                    'default': f'Invalid default value "{self.default}": {err}'
                 })
 
         # Minimum/maximum values can be set only for numeric fields