diff --git a/paynt/verification/property.py b/paynt/verification/property.py
index 17cad1b3..4b83bcb4 100644
--- a/paynt/verification/property.py
+++ b/paynt/verification/property.py
@@ -160,7 +160,7 @@ def can_be_improved(self):
         return False
 
     def negate(self):
-        negated_formula = self.formula.clone()
+        negated_formula = self.property.raw_formula.clone()
         negated_formula.comparison_type = {
             stormpy.ComparisonType.LESS:    stormpy.ComparisonType.GEQ,
             stormpy.ComparisonType.LEQ:     stormpy.ComparisonType.GREATER,
@@ -282,7 +282,7 @@ def can_be_improved(self):
         return not( not self.reward and self.minimizing and self.threshold == 0 )
 
     def negate(self):
-        negated_formula = self.formula.clone()
+        negated_formula = self.property.raw_formula.clone()
         negate_optimality_type = {
             stormpy.OptimizationDirection.Minimize:    stormpy.OptimizationDirection.Maximize,
             stormpy.OptimizationDirection.Maximize:    stormpy.OptimizationDirection.Minimize