diff --git a/Data/Constraint.hs b/Data/Constraint.hs
--- a/Data/Constraint.hs
+++ b/Data/Constraint.hs
@@ -32,6 +32,7 @@
 instance Eq (a :- b) where Sub _ == Sub _ = True
 instance Ord (a :- b) where Sub _ `compare` Sub _ = EQ
 instance Show (a :- b) where showsPrec p (Sub _) = showParen (p > 10) $ showString "Sub Dict"
+instance Semigroup (a :- b) where (<>) = pure
 
 instance Category (:-) where
     id = Sub Dict
diff --git a/constraint.cabal b/constraint.cabal
--- a/constraint.cabal
+++ b/constraint.cabal
@@ -1,5 +1,5 @@
 name:                constraint
-version:             0.1.2.0
+version:             0.1.2.1
 synopsis:            Reified constraints
 -- description:         
 license:             BSD3