diff --git a/Data/Eq/Type.hs b/Data/Eq/Type.hs
--- a/Data/Eq/Type.hs
+++ b/Data/Eq/Type.hs
@@ -97,22 +97,21 @@
 lift3' ab cd ef = lift3 ab . lift2 cd . lift ef
 
 #ifdef LANGUAGE_TypeFamilies
-
-type family Inj f :: *
+type family Inj f
 type instance Inj (f a) = a
 newtype Lower a b = Lower { unlower :: Inj a := Inj b }
 -- | Type constructors are injective, so you can lower equality through any type constructor
 lower :: f a := f b -> a := b
 lower eq = unlower (subst eq (Lower id :: Lower (f a) (f a)))
 
-type family Inj2 f :: *
+type family Inj2 f
 type instance Inj2 (f a b) = a
 newtype Lower2 a b = Lower2 { unlower2 :: Inj2 a := Inj2 b }
 -- | ... in any position
 lower2 :: f a c := f b c -> a := b
 lower2 eq = unlower2 (subst eq (Lower2 id :: Lower2 (f a c) (f a c)))
 
-type family Inj3 f :: *
+type family Inj3 f
 type instance Inj3 (f a b c) = a
 newtype Lower3 a b = Lower3 { unlower3 :: Inj3 a := Inj3 b }
 lower3 :: f a c d := f b c d -> a := b
diff --git a/eq.cabal b/eq.cabal
--- a/eq.cabal
+++ b/eq.cabal
@@ -1,6 +1,6 @@
 name:          eq
 category:      Type System
-version:       0.3.4.3
+version:       0.3.5
 license:       BSD3
 cabal-version: >= 1.6
 license-file:  LICENSE
@@ -17,8 +17,12 @@
   type: git
   location: git://github.com/ekmett/eq.git
 
+flag TypeFamilies
+  default: True
+  manual: False
+
 library
-  other-extensions: 
+  other-extensions:
     CPP
     Rank2Types
     TypeOperators
@@ -30,5 +34,9 @@
 
   exposed-modules:
     Data.Eq.Type
+
+  if flag(TypeFamilies)
+    extensions: TypeFamilies
+    cpp-options: -DLANGUAGE_TypeFamilies
 
   ghc-options: -Wall