diff --git a/cpmpy/solvers/exact.py b/cpmpy/solvers/exact.py
index 96e4441ab..cb974dda0 100644
--- a/cpmpy/solvers/exact.py
+++ b/cpmpy/solvers/exact.py
@@ -203,6 +203,7 @@ def solve(self, time_limit=None, assumptions=None, **kwargs):
 
         # set assumptions
         if assumptions is not None:
+            assumptions = flatlist(assumptions)
             assert all(v.is_bool() for v in assumptions), "Non-Boolean assumptions given to Exact: " + str([v for v in assumptions if not v.is_bool()])
             assump_vals = [int(not isinstance(v, NegBoolView)) for v in assumptions]
             assump_vars = [self.solver_var(v._bv if isinstance(v, NegBoolView) else v) for v in assumptions]
diff --git a/cpmpy/solvers/ortools.py b/cpmpy/solvers/ortools.py
index 2029110f5..920402d38 100644
--- a/cpmpy/solvers/ortools.py
+++ b/cpmpy/solvers/ortools.py
@@ -193,7 +193,7 @@ def solve(self, time_limit=None, assumptions=None, solution_callback=None, **kwa
             self.ort_solver.parameters.max_time_in_seconds = float(time_limit)
 
         if assumptions is not None:
-            ort_assum_vars = self.solver_vars(assumptions)
+            ort_assum_vars = self.solver_vars(flatlist(assumptions))
             # dict mapping ortools vars to CPMpy vars
             self.assumption_dict = {ort_var.Index(): cpm_var for (cpm_var, ort_var) in zip(assumptions, ort_assum_vars)}
             self.ort_model.ClearAssumptions()  # because add just appends
diff --git a/cpmpy/solvers/pumpkin.py b/cpmpy/solvers/pumpkin.py
index 1cbbb7d96..57d2bf306 100644
--- a/cpmpy/solvers/pumpkin.py
+++ b/cpmpy/solvers/pumpkin.py
@@ -47,7 +47,7 @@
 from ..expressions.core import Expression, Comparison, Operator, BoolVal
 from ..expressions.globalconstraints import GlobalConstraint
 from ..expressions.variables import _BoolVarImpl, NegBoolView, _IntVarImpl, _NumVarImpl, intvar, boolvar
-from ..expressions.utils import is_num, is_any_list, get_bounds
+from ..expressions.utils import flatlist, is_num, is_any_list, get_bounds
 from ..transformations.get_variables import get_variables
 from ..transformations.linearize import canonical_comparison
 from ..transformations.normalize import toplevel_list
@@ -151,6 +151,7 @@ def solve(self, time_limit=None, prove=False, proof_name="proof.drcp", proof_loc
 
         elif assumptions is not None:
             assert not prove, "Proof-logging under assumptions is not supported"
+            assumptions = flatlist(assumptions)
             pum_assumptions = [self.to_predicate(a) for a in assumptions]
             self.assump_map = dict(zip(pum_assumptions, assumptions))
             solve_func = self.pum_solver.satisfy_under_assumptions
diff --git a/cpmpy/solvers/pysat.py b/cpmpy/solvers/pysat.py
index 72c920e00..e5b681152 100644
--- a/cpmpy/solvers/pysat.py
+++ b/cpmpy/solvers/pysat.py
@@ -251,6 +251,7 @@ def solve(self, time_limit=None, assumptions=None):
         if assumptions is None:
             pysat_assum_vars = [] # default if no assumptions
         else:
+            assumptions = flatlist(assumptions)
             pysat_assum_vars = self.solver_vars(assumptions)
             self.assumption_vars = assumptions
 
diff --git a/cpmpy/solvers/z3.py b/cpmpy/solvers/z3.py
index 26b84622f..9c40eee7a 100644
--- a/cpmpy/solvers/z3.py
+++ b/cpmpy/solvers/z3.py
@@ -55,7 +55,7 @@
 from ..expressions.globalconstraints import GlobalConstraint, DirectConstraint
 from ..expressions.globalfunctions import GlobalFunction
 from ..expressions.variables import _BoolVarImpl, NegBoolView, _NumVarImpl, _IntVarImpl, intvar
-from ..expressions.utils import is_num, is_any_list, is_bool, is_int, is_boolexpr, eval_comparison
+from ..expressions.utils import flatlist, is_num, is_any_list, is_bool, is_int, is_boolexpr, eval_comparison
 from ..transformations.decompose_global import decompose_in_tree
 from ..transformations.normalize import toplevel_list
 from ..transformations.safening import no_partial_functions
@@ -139,7 +139,7 @@ def native_model(self):
         return self.z3_solver
 
 
-    def solve(self, time_limit=None, assumptions=[], **kwargs):
+    def solve(self, time_limit=None, assumptions=None, **kwargs):
         """
             Call the z3 solver
 
@@ -184,8 +184,12 @@ def solve(self, time_limit=None, assumptions=[], **kwargs):
             self.z3_solver.set(timeout=int(time_limit*1000))
 
 
-        z3_assum_vars = self.solver_vars(assumptions)
-        self.assumption_dict = {z3_var : cpm_var for (cpm_var, z3_var) in zip(assumptions, z3_assum_vars)}
+        if assumptions is not None:
+            assumptions = flatlist(assumptions)
+            z3_assum_vars = self.solver_vars(assumptions)
+            self.assumption_dict = {z3_var : cpm_var for (cpm_var, z3_var) in zip(assumptions, z3_assum_vars)}
+        else:
+            z3_assum_vars = []
 
 
         # call the solver, with parameters
diff --git a/tests/test_solvers.py b/tests/test_solvers.py
index fac298f39..88f5d20c8 100644
--- a/tests/test_solvers.py
+++ b/tests/test_solvers.py
@@ -854,6 +854,9 @@ def test_incremental_assumptions(self, solver):
 
         assert s.solve(assumptions=[])
 
+        # better for user experience: allow to use set of assumptions too
+        assert s.solve(assumptions={x,y})
+
     def test_vars_not_removed(self, solver):
             bvs = cp.boolvar(shape=3)
             m = cp.Model([cp.any(bvs) <= 2])