diff --git a/csound-expression-dynamic.cabal b/csound-expression-dynamic.cabal
--- a/csound-expression-dynamic.cabal
+++ b/csound-expression-dynamic.cabal
@@ -1,5 +1,5 @@
 Name:          csound-expression-dynamic
-Version:       0.0.2
+Version:       0.0.3
 Cabal-Version: >= 1.6
 License:       BSD3
 License-file:  LICENSE
diff --git a/src/Csound/Dynamic/Types/EventList.hs b/src/Csound/Dynamic/Types/EventList.hs
--- a/src/Csound/Dynamic/Types/EventList.hs
+++ b/src/Csound/Dynamic/Types/EventList.hs
@@ -31,7 +31,7 @@
 -- The properties:
 --
 -- > forall a . toCsdEventList (singleCsdEvent a) === CsdEventList 1 [(0, 1, a)]
-class CsdSco f where    
+class Functor f => CsdSco f where    
     -- | Converts a given score representation to the canonical one.
     toCsdEventList :: f a -> CsdEventList a
     -- | Constructs a scores that contains only one event. The event happens immediately and lasts for 1 second.