diff --git a/doc/source/whatsnew/v0.23.0.txt b/doc/source/whatsnew/v0.23.0.txt
index cfe28edd175b6..eda3fba043be9 100644
--- a/doc/source/whatsnew/v0.23.0.txt
+++ b/doc/source/whatsnew/v0.23.0.txt
@@ -887,7 +887,8 @@ Timedelta
 - Bug in :func:`Timedelta.total_seconds()` causing precision errors i.e. ``Timedelta('30S').total_seconds()==30.000000000000004`` (:issue:`19458`)
 - Bug in :func: `Timedelta.__rmod__` where operating with a ``numpy.timedelta64`` returned a ``timedelta64`` object instead of a ``Timedelta`` (:issue:`19820`)
 - Multiplication of :class:`TimedeltaIndex` by ``TimedeltaIndex`` will now raise ``TypeError`` instead of raising ``ValueError`` in cases of length mis-match (:issue`19333`)
--
+- Bug in indexing a :class:`TimedeltaIndex` with a ``np.timedelta64`` object which was raising a ``TypeError`` (:issue:`20393`)
+
 
 Timezones
 ^^^^^^^^^
diff --git a/pandas/core/indexes/timedeltas.py b/pandas/core/indexes/timedeltas.py
index b5a08fc0168e4..9757d775201cc 100644
--- a/pandas/core/indexes/timedeltas.py
+++ b/pandas/core/indexes/timedeltas.py
@@ -829,7 +829,8 @@ def _maybe_cast_slice_bound(self, label, side, kind):
             else:
                 return (lbound + to_offset(parsed.resolution) -
                         Timedelta(1, 'ns'))
-        elif is_integer(label) or is_float(label):
+        elif ((is_integer(label) or is_float(label)) and
+              not is_timedelta64_dtype(label)):
             self._invalid_indexer('slice', label)
 
         return label
diff --git a/pandas/tests/indexing/test_timedelta.py b/pandas/tests/indexing/test_timedelta.py
index 3ad3b771b2ab2..48ea49119356d 100644
--- a/pandas/tests/indexing/test_timedelta.py
+++ b/pandas/tests/indexing/test_timedelta.py
@@ -68,3 +68,15 @@ def test_listlike_setitem(self, value):
         series.iloc[0] = value
         expected = pd.Series([pd.NaT, 1, 2], dtype='timedelta64[ns]')
         tm.assert_series_equal(series, expected)
+
+    @pytest.mark.parametrize('start,stop, expected_slice', [
+        [np.timedelta64(0, 'ns'), None, slice(0, 11)],
+        [np.timedelta64(1, 'D'), np.timedelta64(6, 'D'), slice(1, 7)],
+        [None, np.timedelta64(4, 'D'), slice(0, 5)]])
+    def test_numpy_timedelta_scalar_indexing(self, start, stop,
+                                             expected_slice):
+        # GH 20393
+        s = pd.Series(range(11), pd.timedelta_range('0 days', '10 days'))
+        result = s.loc[slice(start, stop)]
+        expected = s.iloc[expected_slice]
+        tm.assert_series_equal(result, expected)