diff --git a/Card.hs b/Card.hs
index a71b409..b706427 100644
--- a/Card.hs
+++ b/Card.hs
@@ -71,6 +71,9 @@ port f bits = f bits . fromEnum
 contains :: Pack -> Card -> Bool
 contains = port testBit
 
+size :: Pack -> Int
+size = popCount
+
 add :: Pack -> Card -> Pack
 add = port setBit
 
@@ -106,7 +109,7 @@ shuffle l =
 pair :: Card -> Pack -> Maybe (Pack, Pack)
 pair card pack =
   let sameMonthCards = sameMonth card `intersection` pack in
-  case popCount sameMonthCards of
+  case size sameMonthCards of
     0 -> Just (add pack card, empty)
     1 -> Just (difference pack sameMonthCards, add sameMonthCards card)
     _ -> Nothing