diff --git a/src/osqp/tests/nn_test.py b/src/osqp/tests/nn_test.py
index f9a77b3a..6f3f8241 100644
--- a/src/osqp/tests/nn_test.py
+++ b/src/osqp/tests/nn_test.py
@@ -133,7 +133,7 @@ def f(P):
 
         return 0.5 * np.sum(np.square(x_hat - true_x))
 
-    dP_fd = approx_fprime(P.tolil().reshape((1,n*n)), f, epsilon=EPS)
+    dP_fd = approx_fprime(P.toarray().flatten(), f, epsilon=EPS)
     if verbose:
         print('dP_fd: ', np.round(dP_fd, decimals=4))
         print('dP: ', np.round(dP, decimals=4))
@@ -164,7 +164,7 @@ def f(A):
 
         return 0.5 * np.sum(np.square(x_hat - true_x))
 
-    dA_fd = approx_fprime(A.tolil().reshape((1,m*n)), f, epsilon=EPS)
+    dA_fd = approx_fprime(A.toarray().flatten(), f, epsilon=EPS)
     if verbose:
         print('dA_fd: ', np.round(dA_fd, decimals=4))
         print('dA: ', np.round(dA, decimals=4))