diff --git a/checkers.cabal b/checkers.cabal
--- a/checkers.cabal
+++ b/checkers.cabal
@@ -1,5 +1,5 @@
 Name:                checkers
-Version:             0.4.5
+Version:             0.4.6
 Cabal-Version:       >= 1.6
 Synopsis:            Check properties on standard classes and data structures.
 Category:            Testing
diff --git a/src/Test/QuickCheck/Checkers.hs b/src/Test/QuickCheck/Checkers.hs
--- a/src/Test/QuickCheck/Checkers.hs
+++ b/src/Test/QuickCheck/Checkers.hs
@@ -185,6 +185,7 @@
 --   instance EqProp a where (=-=) = eq
 -- E.g.,
 
+instance EqProp ()     where (=-=) = eq
 instance EqProp Bool   where (=-=) = eq
 instance EqProp Char   where (=-=) = eq
 instance EqProp Int    where (=-=) = eq