diff --git a/hasql.cabal b/hasql.cabal
--- a/hasql.cabal
+++ b/hasql.cabal
@@ -1,7 +1,7 @@
 name:
   hasql
 version:
-  0.19.10
+  0.19.11
 category:
   Hasql, Database, PostgreSQL
 synopsis:
diff --git a/library/Hasql/Encoders.hs b/library/Hasql/Encoders.hs
--- a/library/Hasql/Encoders.hs
+++ b/library/Hasql/Encoders.hs
@@ -106,7 +106,7 @@
 -- 
 newtype Params a =
   Params (Params.Params a)
-  deriving (Contravariant, Divisible, Monoid, Semigroup)
+  deriving (Contravariant, Divisible, Decidable, Monoid, Semigroup)
 
 -- |
 -- Encode no parameters.
diff --git a/library/Hasql/Encoders/Params.hs b/library/Hasql/Encoders/Params.hs
--- a/library/Hasql/Encoders/Params.hs
+++ b/library/Hasql/Encoders/Params.hs
@@ -11,7 +11,7 @@
 -- Encoder of some representation of a parameters product.
 newtype Params a =
   Params (Op (DList (LibPQ.Oid, Bool -> Maybe ByteString)) a)
-  deriving (Contravariant, Divisible, Monoid)
+  deriving (Contravariant, Divisible, Decidable, Monoid)
 
 instance Semigroup (Params a)