diff --git a/functor-classes-compat.cabal b/functor-classes-compat.cabal
--- a/functor-classes-compat.cabal
+++ b/functor-classes-compat.cabal
@@ -1,5 +1,5 @@
 name:               functor-classes-compat
-version:            2.0.0.1
+version:            2.0.0.2
 synopsis:           Data.Functor.Classes instances for core packages
 description:
   "Data.Functor.Classes" instances for core packages:
@@ -67,6 +67,11 @@
   default-language: Haskell2010
   ghc-options:      -Wall
 
+  -- self test:
+  -- so instances existence is tested while library is built.
+  hs-source-dirs: test
+  other-modules: SelfTest
+
   -- base and transformer dependencies:
   -- t t: base >= 4.9
   -- t f: transformers >= 0.5
@@ -81,7 +86,7 @@
     else
       build-depends:
           base          >=4.5 && <4.9
-        , transformers  >=0.5 && <0.6
+        , transformers  >=0.5 && <0.7
 
   else
     if flag(base-transformers-2)
diff --git a/test/SelfTest.hs b/test/SelfTest.hs
new file mode 100644
--- /dev/null
+++ b/test/SelfTest.hs
@@ -0,0 +1,30 @@
+module SelfTest () where
+
+import qualified Data.Map
+import qualified Data.Set
+import qualified Data.IntMap
+import qualified Data.Sequence
+import qualified Data.Tree
+
+import Data.Map.Functor.Classes ()
+import Data.Set.Functor.Classes ()
+import Data.IntMap.Functor.Classes ()
+import Data.Sequence.Functor.Classes ()
+import Data.Tree.Functor.Classes ()
+
+import Data.Functor.Classes (eq1)
+
+_test1 :: Bool
+_test1 = eq1 (Data.Map.singleton 'x' 'y') (Data.Map.singleton 'x' 'y')
+
+_test2 :: Bool
+_test2 = eq1 (Data.Set.singleton 'x') (Data.Set.singleton 'x')
+
+_test3 :: Bool
+_test3 = eq1 (Data.IntMap.singleton 1 'y') (Data.IntMap.singleton 1 'y')
+
+_test4 :: Bool
+_test4 = eq1 (Data.Sequence.singleton 'x') (Data.Sequence.singleton 'x')
+
+_test5 :: Bool
+_test5 = eq1 (Data.Tree.Node 'x' []) (Data.Tree.Node 'x' [])