diff --git a/pybamm/solvers/idaklu_solver.py b/pybamm/solvers/idaklu_solver.py
index e9c77cf005..d09a537155 100644
--- a/pybamm/solvers/idaklu_solver.py
+++ b/pybamm/solvers/idaklu_solver.py
@@ -240,7 +240,8 @@ def resfn(t, y, inputs, ydot):
             )
 
         else:
-            jac_y0_t0 = model.jac_rhs_algebraic_eval(t_eval[0], y0, inputs_dict)
+            t0 = 0 if t_eval is None else t_eval[0]
+            jac_y0_t0 = model.jac_rhs_algebraic_eval(t0, y0, inputs_dict)
             if sparse.issparse(jac_y0_t0):
                 def jacfn(t, y, inputs, cj):
                     j = (
diff --git a/tests/unit/test_solvers/test_base_solver.py b/tests/unit/test_solvers/test_base_solver.py
index a96adab593..3ae5770c63 100644
--- a/tests/unit/test_solvers/test_base_solver.py
+++ b/tests/unit/test_solvers/test_base_solver.py
@@ -377,11 +377,18 @@ def exact_diff_b(y, a, b):
 
                 sens = model.jacp_rhs_algebraic_eval(t, y, use_inputs)
 
+                if convert_to_format == "casadi":
+                    sens_a = sens[0]
+                    sens_b = sens[1]
+                else:
+                    sens_a = sens["a"]
+                    sens_b = sens["b"]
+
                 np.testing.assert_allclose(
-                    sens["a"], exact_diff_a(y, inputs["a"], inputs["b"])
+                    sens_a, exact_diff_a(y, inputs["a"], inputs["b"])
                 )
                 np.testing.assert_allclose(
-                    sens["b"], exact_diff_b(y, inputs["a"], inputs["b"])
+                    sens_b, exact_diff_b(y, inputs["a"], inputs["b"])
                 )