diff --git a/Data/HashSet/Base.hs b/Data/HashSet/Base.hs
index 09294203..8c8d0ea4 100644
--- a/Data/HashSet/Base.hs
+++ b/Data/HashSet/Base.hs
@@ -241,7 +241,7 @@ null :: HashSet a -> Bool
 null = H.null . asMap
 {-# INLINE null #-}
 
--- | /O(n)/ Return the number of elements in this set.
+-- | /O(1)/ Return the number of elements in this set.
 size :: HashSet a -> Int
 size = H.size . asMap
 {-# INLINE size #-}