diff --git a/library/cadbiom/models/clause_constraints/mcl/MCLSolutions.py b/library/cadbiom/models/clause_constraints/mcl/MCLSolutions.py
index 5d8c8c70627544fdcdc181adffa1b2663afd723a..6ecf299acd54e8e853181cca31e4fbcca14aea3e 100644
--- a/library/cadbiom/models/clause_constraints/mcl/MCLSolutions.py
+++ b/library/cadbiom/models/clause_constraints/mcl/MCLSolutions.py
@@ -670,9 +670,7 @@ class DimacsFrontierSol(object):
         """
         # Frontier places
         # /!\ Most of the time spent in the constructor is due to this line
-        # Already a frozenset but this attribute must be immutable for __hash__,
-        # cast is a security.
-        self.frontier_values = frozenset(raw_sol.frontier_pos_and_neg_values)
+        self.frontier_values = raw_sol.frontier_pos_and_neg_values
 
         # Activated input/events (clocks)
         # Callable of raw_sol method (avoid to store raw_sol in this object)
@@ -687,7 +685,11 @@ class DimacsFrontierSol(object):
         # - by FrontierSolution.from_dimacs_front_sol()
         # - to accelerate the call of self.nb_activated_frontiers
         # - as a criterion of uniqueness, to do set operations
-        self.activated_frontier_values = raw_sol.extract_activated_frontier_values()
+        # Already a frozenset but this attribute must be immutable for __hash__,
+        # cast is a security.
+        self.activated_frontier_values = frozenset(
+            raw_sol.extract_activated_frontier_values()
+        )
 
         # Pre-compute nb of activated frontiers in the current solution
         # PS: use numpy to accelerate this ? The cast is costly...