diff --git a/tests/python/unittest/test_sparse_operator.py b/tests/python/unittest/test_sparse_operator.py
index 57767c612565..d625dfa7906b 100644
--- a/tests/python/unittest/test_sparse_operator.py
+++ b/tests/python/unittest/test_sparse_operator.py
@@ -181,7 +181,7 @@ def test_sparse_retain():
         num_rows = shape[0]
         rsp, _ = rand_sparse_ndarray(shape=shape, storage_type='row_sparse', density=0.5)
         length = np.random.randint(1, num_rows + 1)
-        idx = random_sample(range(0, num_rows), length)
+        idx = random_sample(list(range(0, num_rows)), length)
         idx.sort()
         dns = rsp.asnumpy()
         tensor_retained_expected = np.zeros(shape)
@@ -198,7 +198,6 @@ def test_sparse_retain():
         check_numeric_gradient(sym, [rsp, indices], grad_nodes=['data'], grad_stype_dict={'data': 'row_sparse'})
 
 
-
 if __name__ == '__main__':
     import nose
     nose.runmodule()