diff --git a/pandas/tests/series/test_analytics.py b/pandas/tests/series/test_analytics.py
index ab5a422d08fe0..ab75dbf1b51cc 100644
--- a/pandas/tests/series/test_analytics.py
+++ b/pandas/tests/series/test_analytics.py
@@ -1097,7 +1097,10 @@ def test_isin(self):
         # comparison array (in_list) must be large enough so that numpy doesn't
         # do a manual masking trick that will avoid this issue altogether
         s = Series(list('abcdefghijk' * 10 ** 5))
-        in_list = [-1, 'a', 'b', 'G', 'Y', 'Z', 'E', 'K', 'E', 'S', 'I', 'R', 'R']*6
+        # If numpy doesn't do the manual comparison/mask, these
+        # unorderable mixed types are what cause the exception in numpy
+        in_list = [-1, 'a', 'b', 'G', 'Y', 'Z', 'E',
+                   'K', 'E', 'S', 'I', 'R', 'R'] * 6
 
         assert s.isin(in_list).sum() == 200000