diff --git a/src/paveit/datamodels/material.py b/src/paveit/datamodels/material.py
index e2e705c..beb1a41 100755
--- a/src/paveit/datamodels/material.py
+++ b/src/paveit/datamodels/material.py
@@ -5,7 +5,7 @@ from mongoengine import *
 
 from .project import Project
 from .usermanagement import Organisation, User
-from .norm_specification import DeliveryGrain
+from .norm_specification import DeliveryGrain, EnumerateBase
 from .enumeration import BitumenCategoryEnum, NormEnum
 
 
@@ -60,7 +60,7 @@ class Asphalt(Material):
 
 # Bitumen 
 
-class BitumenParameterStrassenbaubitumen(EnumerateBase):
+class BitumenParameterStrassenbaubitumen(Material):
     
     penetration = FloatField(min_value=0, max_value=1000)
     softening_point = FloatField(min_value=0, max_value =500)
@@ -77,7 +77,7 @@ class Bitumen(Material):
     category = EnumField(BitumenCategoryEnum, required=True)
     norm = EnumField(NormEnum, default=NormEnum.TLBitumen2019)
     
-    parameter = ReferenceField(EnumerateBase)
+    parameter = ReferenceField(Material)
     limits = LazyReferenceField(EnumerateBase)