diff --git a/src/paveit/datamodels/norm_specification.py b/src/paveit/datamodels/norm_specification.py
index d7e5f7c..c39e5c3 100644
--- a/src/paveit/datamodels/norm_specification.py
+++ b/src/paveit/datamodels/norm_specification.py
@@ -166,7 +166,7 @@ class BitumenParameterLimitsPmB(BitumenParameterLimitsBaseEnum):
         # Elastische Rückstellung 25 °C
     hardening_resistance_elastic_recovery_25deg_unit = StringField('%')
     hardening_resistance_elastic_recovery_25deg_operator = EnumField(RelationalOperatorsEnum, default=RelationalOperatorsEnum.gt)
-    hardening_resistance_elastic_recovery_25deg_min = FloatField(min_value=0, max_value=100)
+    hardening_resistance_elastic_recovery_25deg_min = FloatField(min_value=0, max_value=100, default=None)
     
     # Elastische Rückstellung 10 °C
     hardening_resistance_elastic_recovery_10deg_unit = StringField('%', default='%')