diff --git a/festim/boundary_conditions/dirichlet_bc.py b/festim/boundary_conditions/dirichlet_bc.py
index 6bfe2f466..2ab2d61b6 100644
--- a/festim/boundary_conditions/dirichlet_bc.py
+++ b/festim/boundary_conditions/dirichlet_bc.py
@@ -99,6 +99,10 @@ def create_value(
 
             if "t" in arguments and "x" not in arguments and "T" not in arguments:
                 # only t is an argument
+                if not isinstance(self.value(t=float(t)), (float, int)):
+                    raise ValueError(
+                        f"self.value should return a float or an int, not {type(self.value(t=float(t)))} "
+                    )
                 self.value_fenics = F.as_fenics_constant(
                     mesh=mesh, value=self.value(t=float(t))
                 )
diff --git a/festim/hydrogen_transport_problem.py b/festim/hydrogen_transport_problem.py
index 14a808eaf..dd50acbfb 100644
--- a/festim/hydrogen_transport_problem.py
+++ b/festim/hydrogen_transport_problem.py
@@ -191,7 +191,11 @@ def define_temperature(self):
         # if temperature is callable, process accordingly
         elif callable(self.temperature):
             arguments = self.temperature.__code__.co_varnames
-            if "t" in arguments and "x" not in arguments and "T" not in arguments:
+            if "t" in arguments and "x" not in arguments:
+                if not isinstance(self.temperature(t=float(self.t)), (float, int)):
+                    raise ValueError(
+                        f"self.temperature should return a float or an int, not {type(self.temperature(t=float(self.t)))} "
+                    )
                 # only t is an argument
                 self.temperature_fenics = F.as_fenics_constant(
                     mesh=self.mesh.mesh, value=self.temperature(t=float(self.t))
diff --git a/test/test_dirichlet_bc.py b/test/test_dirichlet_bc.py
index b34cd6a7f..7fff122fa 100644
--- a/test/test_dirichlet_bc.py
+++ b/test/test_dirichlet_bc.py
@@ -226,6 +226,7 @@ def test_callable_x_only():
         lambda x, t: 1.0 + x[0] + t,
         lambda x, t, T: 1.0 + x[0] + t + T,
         lambda x, t: ufl.conditional(ufl.lt(t, 1.0), 100.0 + x[0], 0.0),
+        lambda t: 100.0 if t < 1 else 0.0,
     ],
 )
 def test_integration_with_HTransportProblem(value):
@@ -283,6 +284,32 @@ def test_integration_with_HTransportProblem(value):
     assert np.isclose(computed_value, expected_value)
 
 
+@pytest.mark.parametrize(
+    "value",
+    [
+        lambda t: ufl.conditional(ufl.lt(t, 1.0), 1, 2),
+        lambda t: 1 + ufl.conditional(ufl.lt(t, 1.0), 1, 2.0),
+        lambda t: 2 * ufl.conditional(ufl.lt(t, 1.0), 1, 2.0),
+        lambda t: 2 / ufl.conditional(ufl.lt(t, 1.0), 1, 2.0),
+    ],
+)
+def test_define_value_error_if_ufl_conditional_t_only(value):
+    """Test that a ValueError is raised when the value attribute is a callable
+    of t only and contains a ufl conditional"""
+
+    subdomain = F.SurfaceSubdomain1D(1, x=1)
+    species = F.Species("test")
+
+    bc = F.DirichletBC(subdomain, value, species)
+
+    t = fem.Constant(mesh, 0.0)
+
+    with pytest.raises(
+        ValueError, match="self.value should return a float or an int, not "
+    ):
+        bc.create_value(mesh=mesh, function_space=None, temperature=None, t=t)
+
+
 def test_species_predefined():
     """Test a ValueError is raised when the species defined in the boundary
     condition is not predefined in the model"""
diff --git a/test/test_h_transport_problem.py b/test/test_h_transport_problem.py
index a8dfc570f..ab30b9e77 100644
--- a/test/test_h_transport_problem.py
+++ b/test/test_h_transport_problem.py
@@ -77,6 +77,7 @@ def test_define_temperature_value_error_raised():
         (lambda x: 1.0 + x[0], fem.Function),
         (lambda x, t: 1.0 + x[0] + t, fem.Function),
         (lambda x, t: ufl.conditional(ufl.lt(t, 1.0), 100.0 + x[0], 0.0), fem.Function),
+        (lambda t: 100.0 if t < 1 else 0.0, fem.Constant),
     ],
 )
 def test_define_temperature(input, expected_type):
@@ -97,6 +98,29 @@ def test_define_temperature(input, expected_type):
     assert isinstance(my_model.temperature_fenics, expected_type)
 
 
+@pytest.mark.parametrize(
+    "input",
+    [
+        lambda t: ufl.conditional(ufl.lt(t, 1.0), 1, 2),
+        lambda t: 1 + ufl.conditional(ufl.lt(t, 1.0), 1, 2.0),
+        lambda t: 2 * ufl.conditional(ufl.lt(t, 1.0), 1, 2.0),
+        lambda t: 2 / ufl.conditional(ufl.lt(t, 1.0), 1, 2.0),
+    ],
+)
+def test_define_temperature_error_if_ufl_conditional_t_only(input):
+    """Test that a ValueError is raised when the temperature attribute is a callable
+    of t only and contains a ufl conditional"""
+    my_model = F.HydrogenTransportProblem(mesh=test_mesh)
+    my_model.t = fem.Constant(test_mesh.mesh, 0.0)
+
+    my_model.temperature = input
+
+    with pytest.raises(
+        ValueError, match="self.temperature should return a float or an int, not "
+    ):
+        my_model.define_temperature()
+
+
 def test_iterate():
     """Test that the iterate method updates the solution and time correctly"""
     # BUILD