diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,9 +1,14 @@
-## 0.5.0
+## 0.5.1 [2023-11-19]
 
+- Corrected bug in `XorB` and `EquivB`
+
+
+## 0.5.0 [2023-11-19]
+
 - Four monoid structures for a boolean algebra (`AnyB`, `AllB`, `XorB`, `EquivB`)
 - Typeclass altered so that {or, and, nor, nand, any, all} are no longer members
 - Add instances for `()` and `(a,b,c)`
-- `minimal` pragma (and corresponding definition)
+- `minimal` pragma (and corresponding documentation)
 - The opposite Boolean algebra (exchanging `true` and `false`, `&&` and `||`, etc)
 - A more general instance for `Endo`
 - Tested with GHC 7.0 - 9.6
diff --git a/cond.cabal b/cond.cabal
--- a/cond.cabal
+++ b/cond.cabal
@@ -1,6 +1,6 @@
 Cabal-Version: >= 1.10
 Name: cond
-Version: 0.5.0
+Version: 0.5.1
 Synopsis: Basic conditional and boolean operators with monadic variants.
 Category: Control, Logic, Monad
 License: BSD3
diff --git a/src/Data/Algebra/Boolean.hs b/src/Data/Algebra/Boolean.hs
--- a/src/Data/Algebra/Boolean.hs
+++ b/src/Data/Algebra/Boolean.hs
@@ -150,8 +150,8 @@
 -- | `stimes` for a group of exponent 2
 stimesPeriod2 :: (Monoid a, Integral n) => n -> a -> a
 stimesPeriod2 n x
-  | even n    = x
-  | otherwise = mempty
+  | even n    = mempty
+  | otherwise = x
 
 -- | A boolean algebra regarded as a monoid under exclusive or
 newtype XorB b = XorB {