diff --git a/pybamm/expression_tree/operations/evaluate_python.py b/pybamm/expression_tree/operations/evaluate_python.py
index ec8f59fb4b..5efbda5aab 100644
--- a/pybamm/expression_tree/operations/evaluate_python.py
+++ b/pybamm/expression_tree/operations/evaluate_python.py
@@ -624,8 +624,8 @@ def get_jacobian(self):
     def get_sensitivities(self):
         n = len(self._arg_list)
 
-        # forward mode autodiff wrt inputs, which is argument 3 after arg_list
-        jacobian_evaluate = jax.jacfwd(self._evaluate_jax, argnums=3 + n)
+        # forward mode autodiff wrt inputs, which is argument 2 after arg_list
+        jacobian_evaluate = jax.jacfwd(self._evaluate_jax, argnums=2 + n)
 
         self._sens_evaluate = jax.jit(
             jacobian_evaluate, static_argnums=self._static_argnums
diff --git a/pybamm/solvers/base_solver.py b/pybamm/solvers/base_solver.py
index c7981719e8..e5efb8f251 100644
--- a/pybamm/solvers/base_solver.py
+++ b/pybamm/solvers/base_solver.py
@@ -320,11 +320,9 @@ def report(string):
                         )
                     )
                     jacp = func.get_sensitivities()
-                    jacp = jacp.evaluate
                 if use_jacobian:
                     report(f"Calculating jacobian for {name} using jax")
                     jac = func.get_jacobian()
-                    jac = jac.evaluate
                 else:
                     jac = None
 
@@ -342,17 +340,17 @@ def report(string):
                         p: symbol.diff(pybamm.InputParameter(p))
                         for p in model.calculate_sensitivities
                     }
-                    if model.convert_to_format == "python":
-                        report(f"Converting sensitivities for {name} to python")
-                        jacp_dict = {
-                            p: pybamm.EvaluatorPython(jacp)
-                            for p, jacp in jacp_dict.items()
-                        }
+
+                    report(f"Converting sensitivities for {name} to python")
+                    jacp_dict = {
+                        p: pybamm.EvaluatorPython(jacp)
+                        for p, jacp in jacp_dict.items()
+                    }
 
                     # jacp should be a function that returns a dict of sensitivities
                     def jacp(*args, **kwargs):
                         return {
-                            k: v.evaluate(*args, **kwargs) for k, v in jacp_dict.items()
+                            k: v(*args, **kwargs) for k, v in jacp_dict.items()
                         }
 
                 else:
@@ -452,8 +450,8 @@ def jacp(*args, **kwargs):
                     jacp_dict = {}
                     for pname in model.calculate_sensitivities:
                         p_diff = casadi.jacobian(casadi_expression, p_casadi[pname])
-                        jacp_dict[pname] = casadi.casadi_expressiontion(
-                            name, [t_casadi, y_casadi, p_casadi_stacked], [p_diff]
+                        jacp_dict[pname] = casadi.Function(
+                            name, [t_casadi, y_and_S, p_casadi_stacked], [p_diff]
                         )
 
                     # jacp should be a casadi_expressiontion that returns
diff --git a/tests/unit/test_solvers/test_base_solver.py b/tests/unit/test_solvers/test_base_solver.py
index 9d5bcd9bce..5222f01801 100644
--- a/tests/unit/test_solvers/test_base_solver.py
+++ b/tests/unit/test_solvers/test_base_solver.py
@@ -375,7 +375,8 @@ def exact_diff_b(y, a, b):
                 else:
                     use_inputs = inputs
 
-                sens = model.sensitivities_eval(t, y, use_inputs)
+                sens = model.jacp_rhs_algebraic_eval(t, y, use_inputs)
+
                 np.testing.assert_allclose(
                     sens["a"], exact_diff_a(y, inputs["a"], inputs["b"])
                 )