diff --git a/ortools/sat/python/cp_model.py b/ortools/sat/python/cp_model.py
index 9cf9443f96..78fd14971f 100644
--- a/ortools/sat/python/cp_model.py
+++ b/ortools/sat/python/cp_model.py
@@ -1716,17 +1716,20 @@ def add_allowed_assignments(
                 "add_allowed_assignments expects a non-empty variables array"
             )
 
-        ct = Constraint(self)
+        ct: Constraint = Constraint(self)
         model_ct = self.__model.constraints[ct.index]
         model_ct.table.vars.extend([self.get_or_make_index(x) for x in variables])
-        arity = len(variables)
+        arity: int = len(variables)
         for t in tuples_list:
             if len(t) != arity:
                 raise TypeError("Tuple " + str(t) + " has the wrong arity")
-            ar = []
-            for v in t:
-                ar.append(cmh.assert_is_int64(v))
-            model_ct.table.values.extend(ar)
+
+        # duck-typing (no explicit type checks here)
+        try:
+            model_ct.table.values.extend(a for b in tuples_list for a in b)
+        except ValueError as ex:
+            raise TypeError(f"add_xxx_assignment: Not an integer or does not fit in an int64_t: {ex.args}") from ex
+
         return ct
 
     def add_forbidden_assignments(
@@ -1760,7 +1763,7 @@ def add_forbidden_assignments(
             )
 
         index = len(self.__model.constraints)
-        ct = self.add_allowed_assignments(variables, tuples_list)
+        ct: Constraint = self.add_allowed_assignments(variables, tuples_list)
         self.__model.constraints[index].table.negated = True
         return ct
 
@@ -2751,7 +2754,7 @@ def get_interval_var_from_proto_index(self, index: int) -> IntervalVar:
 
     # Helpers.
 
-    def __str__(self):
+    def __str__(self) -> str:
         return str(self.__model)
 
     @property