diff --git a/iteratee.cabal b/iteratee.cabal
--- a/iteratee.cabal
+++ b/iteratee.cabal
@@ -1,5 +1,5 @@
 name:          iteratee
-version:       0.8.7.3
+version:       0.8.7.4
 synopsis:      Iteratee-based I/O
 description:
   The Iteratee monad provides strict, safe, and functional I/O. In addition
diff --git a/src/Data/Iteratee/Iteratee.hs b/src/Data/Iteratee/Iteratee.hs
--- a/src/Data/Iteratee/Iteratee.hs
+++ b/src/Data/Iteratee/Iteratee.hs
@@ -439,10 +439,10 @@
 --  which transforms stream of @s@ to stream
 --  of @s'@ to into Enumerator which produces stream of @s'@
 ($=)
-  :: (Nullable s1, Nullable s2, Monad m)
-  => (forall a. Enumerator s1 m a)
-  -> Enumeratee s1 s2 m b
-  -> Enumerator s2 m b
+  :: (Nullable s, Nullable s', Monad m)
+  => (forall a. Enumerator s m a)
+  -> Enumeratee s s' m b
+  -> Enumerator s' m b
 ($=) enum enee iter = enum (enee iter) >>= run