diff --git a/src/ZEO/tests/testZEO.py b/src/ZEO/tests/testZEO.py
index 51525d317..614e089d6 100644
--- a/src/ZEO/tests/testZEO.py
+++ b/src/ZEO/tests/testZEO.py
@@ -489,6 +489,8 @@ def getConfig(self):
 
 class FileStorageClientHexTests(FileStorageHexTests):
 
+    use_extension_bytes = True
+
     def getConfig(self):
         return """\
         %import ZODB.tests