diff --git a/acid-state.cabal b/acid-state.cabal
--- a/acid-state.cabal
+++ b/acid-state.cabal
@@ -7,7 +7,7 @@
 -- The package version. See the Haskell package versioning policy
 -- (http://www.haskell.org/haskellwiki/Package_versioning_policy) for
 -- standards guiding when and how versions should be incremented.
-Version:             0.6.6
+Version:             0.7.0
 
 -- A short (one-line) description of the package.
 Synopsis:            Add ACID guarantees to any serializable Haskell data structure.
diff --git a/src/Data/Acid/Core.hs b/src/Data/Acid/Core.hs
--- a/src/Data/Acid/Core.hs
+++ b/src/Data/Acid/Core.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE GADTs, DeriveDataTypeable, TypeFamilies,
+{-# LANGUAGE CPP, GADTs, DeriveDataTypeable, TypeFamilies,
              FlexibleContexts, BangPatterns #-}
 -----------------------------------------------------------------------------
 -- |
@@ -48,7 +48,7 @@
 
 import Data.Typeable                      ( Typeable, typeOf )
 import Unsafe.Coerce                      ( unsafeCoerce )
-
+import Data.Typeable.Internal
 
 -- | The basic Method class. Each Method has an indexed result type
 --   and a unique tag.
@@ -58,7 +58,22 @@
     type MethodResult ev
     type MethodState ev
     methodTag :: ev -> Tag
-    methodTag ev = Lazy.pack (show (typeOf ev))
+    methodTag ev = Lazy.pack (showQualifiedTypeRep (typeOf ev))
+
+#if MIN_VERSION_base(4,4,0)
+-- in base >= 4.4 the Show instance for TypeRep no longer provides a
+-- fully qualified name. But we have old data around that expects the
+-- FQN. So we will recreate the old naming system for newer versions
+-- of base. We could do something better, but happstack-state is
+-- end-of-life anyway.
+showQualifiedTypeRep :: TypeRep -> String
+showQualifiedTypeRep tr =
+    let (TypeRep _f con _rep) = tr
+    in tyConModule con ++ "." ++ show tr
+#else
+showQualifiedTypeRep :: TypeRep -> String
+showQualifiedTypeRep tr = show tr
+#endif
 
 -- | The control structure at the very center of acid-state.
 --   This module provides access to a mutable state through