diff --git a/nilmdb/utils/interval.py b/nilmdb/utils/interval.py
index 5b5d7b4..df37b9c 100644
--- a/nilmdb/utils/interval.py
+++ b/nilmdb/utils/interval.py
@@ -98,7 +98,7 @@ def _interval_math_helper(a, b, op, subset = True):
             in_b = True
         elif k == 2:
             in_a = False
-        elif k == 3:
+        else: # k == 3
             in_b = False
         include = op(in_a, in_b)
         if include and out_start is None: