diff --git a/jass/test/test_worktable.py b/jass/test/test_worktable.py
index 080a5d46b8afb0a854e9058b02215a74d38e6491..2c3b77484a1511b6b24c631a4da55fa5203ab93c 100644
--- a/jass/test/test_worktable.py
+++ b/jass/test/test_worktable.py
@@ -22,9 +22,9 @@ class TestWorkTable(object):
         cls.expected_hdf_path = cls.get_file_path_fn('worktable.hdf5')
         create_worktable_file(cls.phenotypes_sel, init_file_path, cls.result_hdf_path, cls.remove_nan)
         cls.expected_sumstatjosttab = read_hdf(cls.expected_hdf_path, 'SumStatJostTab')
-        cls.expected_sumstatjosttab.reset_index(drop=True)
+        cls.expected_sumstatjosttab.reset_index(drop=True, inplace=True)
         cls.result_sumstatjosttab = read_hdf(cls.result_hdf_path, 'SumStatJostTab')
-        cls.result_sumstatjosttab.reset_index(drop=True)
+        cls.result_sumstatjosttab.reset_index(drop=True, inplace=True)
         cls.expected_regionsubtable = read_hdf(cls.expected_hdf_path, 'RegionSubTable')
         cls.result_regionsubtable = read_hdf(cls.result_hdf_path, 'RegionSubTable')
         cls.expected_summarytable = read_hdf(cls.expected_hdf_path, 'summaryTable')