diff --git a/filip/models/ngsi_v2/units.py b/filip/models/ngsi_v2/units.py
index 68bf6c86..4410952f 100644
--- a/filip/models/ngsi_v2/units.py
+++ b/filip/models/ngsi_v2/units.py
@@ -136,6 +136,8 @@ class Unit(BaseModel):
     class Config:
         extra = 'ignore'
         allow_population_by_field_name = True
+        allow_mutation = False
+        frozen = True
 
     @root_validator(pre=False, allow_reuse=True)
     def check_consistency(cls, values):