diff --git a/language-ats.cabal b/language-ats.cabal
--- a/language-ats.cabal
+++ b/language-ats.cabal
@@ -1,5 +1,5 @@
 name:                language-ats
-version:             1.0.1.0
+version:             1.0.1.1
 synopsis:            Parser and pretty-printer for ATS.
 description:         Parser and pretty-printer for [ATS](http://www.ats-lang.org/), written with Happy and Alex.
 license:             BSD3
diff --git a/src/Language/ATS/Types.hs b/src/Language/ATS/Types.hs
--- a/src/Language/ATS/Types.hs
+++ b/src/Language/ATS/Types.hs
@@ -267,8 +267,7 @@
 
 -- | A (possibly effectful) expression.
 data Expression a = Let a (ATS a) (Maybe (Expression a))
-                  | VoidLiteral -- ^ The '()' literal representing inaction.
-                      a
+                  | VoidLiteral a -- ^ The '()' literal representing inaction.
                   | Call (Name a) [[Type a]] [Type a] (Maybe [Expression a]) [Expression a]
                   | NamedVal (Name a)
                   | ListLiteral a String (Type a) [Expression a]