diff --git a/composite-aeson.cabal b/composite-aeson.cabal
--- a/composite-aeson.cabal
+++ b/composite-aeson.cabal
@@ -3,7 +3,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           composite-aeson
-version:        0.4.1.0
+version:        0.4.2.0
 synopsis:       JSON for Vinyl/Frames records
 description:    Integration between Aeson and Vinyl/Frames records allowing records to be easily converted to JSON using automatic derivation, explicit formats, or a mix of both.
 category:       Records
@@ -22,6 +22,7 @@
   ghc-options: -Wall -O2
   build-depends:
       base >= 4.7 && < 5
+    , mtl
     , aeson
     , aeson-better-errors
     , composite-base
@@ -30,6 +31,8 @@
     , generic-deriving
     , hashable
     , lens
+    , mmorph
+    , mtl
     , profunctors
     , scientific
     , tagged
@@ -63,6 +66,7 @@
   ghc-options: -Wall -O2 -threaded -rtsopts -with-rtsopts=-N -fno-warn-orphans
   build-depends:
       base >= 4.7 && < 5
+    , mtl
     , aeson
     , aeson-better-errors
     , composite-base
@@ -71,6 +75,8 @@
     , generic-deriving
     , hashable
     , lens
+    , mmorph
+    , mtl
     , profunctors
     , scientific
     , tagged
@@ -85,6 +91,7 @@
     , composite-aeson
     , hspec
   other-modules:
+      EnumSpec
       RecordSpec
       TupleSpec
   default-language: Haskell2010
diff --git a/src/Composite/Aeson/Base.hs b/src/Composite/Aeson/Base.hs
--- a/src/Composite/Aeson/Base.hs
+++ b/src/Composite/Aeson/Base.hs
@@ -1,14 +1,17 @@
 module Composite.Aeson.Base
   ( ToJson(..), FromJson(..), JsonProfunctor(..), _JsonProfunctor, JsonFormat(..)
   , toJsonWithFormat, fromJsonWithFormat, parseJsonWithFormat, parseJsonWithFormat'
-  , dimapJsonFormat, jsonFormatWithIso, wrappedJsonFormat
+  , dimapJsonFormat, jsonFormatWithIso, wrapJsonFormat, jsonFormatWithoutCustomError, wrappedJsonFormat
   ) where
 
-import Control.Lens (AnIso', Iso, Wrapped(type Unwrapped), _Wrapped', _Wrapped, iso, over, withIso)
+import Control.Lens (AnIso', Iso, _2, Wrapped(type Unwrapped), _Wrapped', _Wrapped, iso, over, withIso)
 import Control.Lens.TH (makeWrapped)
+import Control.Monad.Except (withExceptT)
+import Control.Monad.Morph (hoist)
 import qualified Data.Aeson as Aeson
 import qualified Data.Aeson.Types as Aeson
 import qualified Data.Aeson.BetterErrors as ABE
+import qualified Data.Aeson.BetterErrors.Internal as ABEI
 import Data.Functor.Contravariant (Contravariant, contramap)
 import Data.Profunctor (Profunctor(dimap))
 import Data.Text (Text)
@@ -83,6 +86,44 @@
 -- |Wrap a 'JsonFormat' for type @a@ in a pair of functions representing an isomorphism between @a@ and @b@ to produce a new @JsonFormat@ for @b@.
 dimapJsonFormat :: (b -> a) -> (a -> b) -> JsonFormat e a -> JsonFormat e b
 dimapJsonFormat f g = over _Wrapped (dimap f g)
+
+-- |Given a @'JsonFormat' e a@ and a pair of functions @b -> a@ and @a -> Either e b@, produce a @'JsonFormat' e b@.
+--
+-- This is for the common case of a @newtype@ wrapper which asserts some kind of validation has been done, e.g.:
+--
+-- @
+--   newtype MyType = MyType { unMyType :: Int }
+--
+--   mkMyType :: Int -> Either Text MyType
+--   mkMyType i | i <= 0    = Left "must be positive!"
+--              | otherwise = Right (MyType i)
+--
+--   myTypeJsonFormat :: JsonFormat e MyType
+--   myTypeJsonFormat = wrapJsonFormat intJsonFormat mkMyType unMyType
+-- @
+wrapJsonFormat :: JsonFormat e a -> (a -> Either e b) -> (b -> a) -> JsonFormat e b
+wrapJsonFormat (JsonFormat (JsonProfunctor oa ia)) ab ba = JsonFormat (JsonProfunctor ob ib)
+  where
+    ob = oa . ba
+    ib = either ABE.throwCustomError pure . ab =<< ia
+
+-- |Take a 'JsonFormat' which produces some 'Show'-able custom error and convert any custom errors into Aeson 'fail' style errors. Since the custom errors
+-- are never generated by the resulting 'JsonFormat', any custom error type can be assumed.
+--
+-- This is commonly used to take a more specific @'JsonFormat' MyError MyType@ and make it a more generic @'JsonFormat' e MyType@, e.g. to be used as a 
+-- 'Composite.Aeson.Default.defaultJsonFormat'.
+jsonFormatWithoutCustomError :: Show e => JsonFormat e a -> JsonFormat e' a
+jsonFormatWithoutCustomError =
+  over (_Wrapped . _JsonProfunctor . _2 . _Wrapped) $
+    ABEI.mapParseT $ hoist $ withExceptT $ \ case
+        ABEI.BadSchema pos (ABEI.KeyMissing k)       -> ABEI.BadSchema pos (ABEI.KeyMissing k)
+        ABEI.BadSchema pos (ABEI.OutOfBounds i)      -> ABEI.BadSchema pos (ABEI.OutOfBounds i)
+        ABEI.BadSchema pos (ABEI.WrongType t v)      -> ABEI.BadSchema pos (ABEI.WrongType t v)
+        ABEI.BadSchema pos (ABEI.ExpectedIntegral d) -> ABEI.BadSchema pos (ABEI.ExpectedIntegral d)
+        ABEI.BadSchema pos (ABEI.FromAeson e)        -> ABEI.BadSchema pos (ABEI.FromAeson e)
+        ABEI.BadSchema pos (ABEI.CustomError e)      -> ABEI.BadSchema pos (ABEI.FromAeson (show e))
+
+        ABEI.InvalidJSON msg -> ABEI.InvalidJSON msg
 
 -- |Wrap a 'JsonFormat' for type @a@ in an isomorphism to produce a new @JsonFormat@ for @b@.
 jsonFormatWithIso :: AnIso' b a -> JsonFormat e a -> JsonFormat e b
diff --git a/src/Composite/Aeson/Enum.hs b/src/Composite/Aeson/Enum.hs
--- a/src/Composite/Aeson/Enum.hs
+++ b/src/Composite/Aeson/Enum.hs
@@ -1,5 +1,6 @@
 module Composite.Aeson.Enum where
 
+import Control.Monad.Error.Class (throwError)
 import Composite.Aeson.Base (JsonFormat(JsonFormat), JsonProfunctor(JsonProfunctor))
 import qualified Data.Aeson as Aeson
 import qualified Data.Aeson.BetterErrors as ABE
@@ -48,6 +49,7 @@
     fromJson = do
       t <- ABE.asText
       case lookupText t of
-        Nothing -> fail $ "expected " ++ expectedText ++ ", not " ++ unpack t
+        Nothing -> throwError $ ABE.BadSchema [] $ ABE.FromAeson $
+                     "expected " ++ expectedText ++ ", not " ++ unpack t
         Just v  -> pure v
   
diff --git a/src/Composite/Aeson/Formats/DateTime.hs b/src/Composite/Aeson/Formats/DateTime.hs
--- a/src/Composite/Aeson/Formats/DateTime.hs
+++ b/src/Composite/Aeson/Formats/DateTime.hs
@@ -7,6 +7,8 @@
 import Composite.Aeson.Base (JsonFormat(JsonFormat), JsonProfunctor(JsonProfunctor))
 import Composite.Aeson.DateTimeFormatUtils (fixupTzIn, fixupTzOut, fixupMs)
 import Composite.Aeson.Formats.Provided (stringJsonFormat)
+import Control.Monad.Error.Class (throwError)
+import qualified Data.Aeson.BetterErrors as ABE
 import Data.Either (partitionEithers)
 import Data.Monoid ((<>))
 import Data.List (intercalate)
@@ -46,11 +48,12 @@
         (_, a : _) ->
           pure a
         (es, _) | null otherInFormats ->
-          fail $ "expected date/time string formatted as " <> dateTimeFormatExample outFormat <> ", but: " <> intercalate ", " es
+          toss $ "expected date/time string formatted as " <> dateTimeFormatExample outFormat <> ", but: " <> intercalate ", " es
         (es, _) ->
-          fail $ "expected date/time string formatted as one of "
+          toss $ "expected date/time string formatted as one of "
               <> intercalate ", " (map dateTimeFormatExample formatsList)
               <> ", but: " <> intercalate ", " es
+    toss = throwError . ABE.BadSchema [] . ABE.FromAeson
 
 -- |ISO8601 extended date format (@yyyy-mm-dd@).
 iso8601DateJsonFormat :: JsonFormat e Day
diff --git a/src/Composite/Aeson/Formats/Generic.hs b/src/Composite/Aeson/Formats/Generic.hs
--- a/src/Composite/Aeson/Formats/Generic.hs
+++ b/src/Composite/Aeson/Formats/Generic.hs
@@ -6,6 +6,7 @@
 import Composite.Aeson.Base (JsonFormat(JsonFormat), JsonProfunctor(JsonProfunctor), FromJson(FromJson))
 import Control.Arrow (second)
 import Control.Lens (_Wrapped, over, unsnoc)
+import Control.Monad.Error.Class (throwError)
 import Data.Aeson (FromJSON, ToJSON, (.=), toJSON)
 import qualified Data.Aeson as Aeson
 import qualified Data.Aeson.BetterErrors as ABE
@@ -185,7 +186,8 @@
       t <- ABE.key typeField ABE.asText
       case lookup t (NEL.toList iAs) of
         Just (FromJson iA) -> ABE.key valueField iA
-        Nothing -> fail $ "expected " <> unpack typeField <> " to be one of " <> expected
+        Nothing -> toss $ "expected " <> unpack typeField <> " to be one of " <> expected
+    toss = throwError . ABE.BadSchema [] . ABE.FromAeson
 
 -- |'JsonFormat' which maps sum types to JSON in the 'SumStyleMergeType' style.
 jsonMergeTypeSumFormat :: Text -> (a -> (Text, Aeson.Value)) -> NonEmpty (Text, FromJson e a) -> JsonFormat e a
@@ -206,4 +208,5 @@
       t <- ABE.key typeField ABE.asText
       case lookup t (NEL.toList iAs) of
         Just (FromJson iA) -> iA
-        Nothing -> fail $ "expected " <> unpack typeField <> " to be one of " <> expected
+        Nothing -> toss $ "expected " <> unpack typeField <> " to be one of " <> expected
+    toss = throwError . ABE.BadSchema [] . ABE.FromAeson
diff --git a/test/EnumSpec.hs b/test/EnumSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/EnumSpec.hs
@@ -0,0 +1,23 @@
+{-# LANGUAGE DeriveGeneric #-}
+module EnumSpec where
+
+import Data.Void (Void)
+import Data.Aeson (Value(String))
+import GHC.Generics (Generic)
+import Composite.Aeson.Base (JsonFormat, fromJsonWithFormat)
+import Composite.Aeson.Enum (enumJsonFormat)
+import qualified Data.Aeson.BetterErrors as ABE
+import Test.Hspec (Spec, describe, it, shouldBe)
+
+data TestEnum = A | B deriving (Show, Eq, Ord, Generic)
+
+testEnumFormat :: JsonFormat Void TestEnum
+testEnumFormat = enumJsonFormat ""
+
+enumSuite :: Spec
+enumSuite =
+  describe "enumJsonFormat" $
+    describe "when input value does not match any of enum constructors" $
+      it "should return a parse error, not throw an exception" $
+        ABE.parseValue (fromJsonWithFormat testEnumFormat) (String "C")
+          `shouldBe` Left (ABE.BadSchema [] (ABE.FromAeson "expected one of A, B, not C"))
diff --git a/test/Main.hs b/test/Main.hs
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -1,9 +1,10 @@
 import RecordSpec (recordSuite)
 import TupleSpec (tupleSuite)
+import EnumSpec (enumSuite)
 import Test.Hspec (hspec)
 
 main :: IO ()
 main = hspec $ do
   recordSuite
   tupleSuite
-
+  enumSuite