diff --git a/tests/testutil.py b/tests/testutil.py
index 9963f75ed7d5fe5fde361683b6cdce7ff42defe7..01060048b347633db284e18db050ae8a22e4ce92 100644
--- a/tests/testutil.py
+++ b/tests/testutil.py
@@ -44,9 +44,15 @@ def check_post_meta(txn, *expected_meta, default=None):
             assert actual == expected
 
 def combine_values(*value_seqs):
+    stop = 0
+    for seq in value_seqs:
+        try:
+            stop = max(stop, len(seq))
+        except TypeError:
+            pass
     return itertools.islice(
         zip(*(itertools.cycle(seq) for seq in value_seqs)),
-        max(len(seq) for seq in value_seqs),
+        stop,
     )
 
 def parse_date(s, fmt='%Y-%m-%d'):