diff --git a/reviewboard/reviews/fields.py b/reviewboard/reviews/fields.py
index 6193626686f7e28cfce64131937bad3bf2ed45a6..c534c45e03afb73e1fd2b65b7b0ab0848dd43036 100644
--- a/reviewboard/reviews/fields.py
+++ b/reviewboard/reviews/fields.py
@@ -29,7 +29,7 @@ class BaseReviewRequestFieldSet(object):
     fieldset_id = None
     label = None
     show_required = False
-    field_classes = []
+    field_classes = None
     tag_name = None
 
     def __init__(self, review_request_details):
@@ -548,6 +548,12 @@ def register_review_request_fieldset(fieldset):
 
     _fieldsets[fieldset_id] = fieldset
 
+    # Set the field_classes to an empty list by default if it doesn't
+    # explicitly provide its own, so that entries don't go into
+    # BaseReviewRequestFieldSet's global list.
+    if field_cls.field_classes is None:
+        field_cls.field_classes = []
+
     for field_cls in fieldset.field_classes:
         _register_field(field_cls)