diff --git a/sets.cabal b/sets.cabal
--- a/sets.cabal
+++ b/sets.cabal
@@ -1,13 +1,11 @@
-cabal-version: 1.12
-
--- This file has been generated from package.yaml by hpack version 0.31.0.
+-- This file has been generated from package.yaml by hpack version 0.21.2.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 43dfe0d613b8c2ccf7c76fdb2b07db2e683eda310038bdcc33fe5108a6ce8f4f
+-- hash: 9b097802837c1541d33b7338721f7e72c397c26e7eb80b8148a1a0299dac9450
 
 name:           sets
-version:        0.0.6
+version:        0.0.6.1
 synopsis:       Ducktyped set interface for Haskell containers.
 description:    Please see the README on Github at <https://github.com/athanclark/sets#readme>
 category:       Data
@@ -19,6 +17,8 @@
 license:        BSD3
 license-file:   LICENSE
 build-type:     Simple
+cabal-version:  >= 1.10
+
 extra-source-files:
     README.md
 
diff --git a/src/Data/Set/Unordered/Many.hs b/src/Data/Set/Unordered/Many.hs
--- a/src/Data/Set/Unordered/Many.hs
+++ b/src/Data/Set/Unordered/Many.hs
@@ -106,7 +106,7 @@
 
 -- | /O(n)/
 delete :: Eq a => a -> UMSet a -> UMSet a
-delete x (UMSet xs) = UMSet $ List.filter (== x) xs
+delete x (UMSet xs) = UMSet $ List.filter (/= x) xs
 
 -- * Combine