diff --git a/qc-tests/Tests.hs b/qc-tests/Tests.hs
index e4eb7b1..8fc3468 100644
--- a/qc-tests/Tests.hs
+++ b/qc-tests/Tests.hs
@@ -20,8 +20,8 @@ import Test.SmartCheck.Types
 
 --------------------------------------------------------------------------------
 
-deriving instance Generic a =>  Generic (Tree a)
-instance (SubTypes a, Generic a) => SubTypes (Tree a)
+deriving instance Generic (Tree a)
+instance (SubTypes a) => SubTypes (Tree a)
 
 instance Q.Arbitrary a => Q.Arbitrary (Tree a) where
   arbitrary = Q.sized mkT
diff --git a/src/Test/SmartCheck/Types.hs b/src/Test/SmartCheck/Types.hs
index 6b6d50b..414f421 100644
--- a/src/Test/SmartCheck/Types.hs
+++ b/src/Test/SmartCheck/Types.hs
@@ -253,10 +253,30 @@ instance (Show a, Q.Arbitrary a, SubTypes a, Typeable a) => GST (K1 i a) where
 -- http://hackage.haskell.org/packages/archive/QuickCheck/2.4.2/doc/html/Test-QuickCheck-Arbitrary.html
 
 instance SubTypes Bool    where baseType _    = True
-instance SubTypes Char    where baseType _    = True
-instance SubTypes Double  where baseType _    = True
-instance SubTypes Float   where baseType _    = True
-instance SubTypes Int     where baseType _    = True
+instance SubTypes Char where
+  subTypes _    = []
+  baseType _    = True
+  replaceChild  = replaceChild'
+  toConstr      = toConstr'
+  showForest    = showForest'
+instance SubTypes Double  where
+  subTypes _    = []
+  baseType _    = True
+  replaceChild  = replaceChild'
+  toConstr      = toConstr'
+  showForest    = showForest'
+instance SubTypes Float   where
+  subTypes _    = []
+  baseType _    = True
+  replaceChild  = replaceChild'
+  toConstr      = toConstr'
+  showForest    = showForest'
+instance SubTypes Int where
+  subTypes _    = []
+  baseType _    = True
+  replaceChild  = replaceChild'
+  toConstr      = toConstr'
+  showForest    = showForest'
 instance SubTypes Integer where
   subTypes _    = []
   baseType _    = True