diff --git a/src/Foreign/Rust/External/JSON.hs b/src/Foreign/Rust/External/JSON.hs
index e8ad823..3318f4c 100644
--- a/src/Foreign/Rust/External/JSON.hs
+++ b/src/Foreign/Rust/External/JSON.hs
@@ -16,6 +16,8 @@ module Foreign.Rust.External.JSON (
   ) where
 
 import Codec.Borsh
+import Foreign.Rust.Failure
+import GHC.Stack
 
 import qualified Data.Aeson           as Aeson
 import qualified Data.Aeson.Encoding  as Aeson (unsafeToEncoding)
@@ -32,13 +34,13 @@ newtype JSON = JSON Lazy.ByteString
   deriving stock (Eq)
   deriving newtype (BorshSize, ToBorsh, FromBorsh)
 
--- | Types with an external JSON renderer (typically, in Rust)
+-- | Types with a Rust-side JSON renderer
 class ToJSON a where
   toJSON :: a -> JSON
 
--- | Types with an external JSON parser (typically, in Rust)
+-- | Types with a Rust-side JSON parser
 class FromJSON a where
-  fromJSON :: JSON -> Either String a
+  fromJSON :: HasCallStack => JSON -> Either Failure a
 
 {-------------------------------------------------------------------------------
   Deriving-via: derive Aeson instances using external (de)serialiser
@@ -67,6 +69,6 @@ instance ToJSON a => Aeson.ToJSON (UseExternalJSON a) where
 instance FromJSON a => Aeson.FromJSON (UseExternalJSON a) where
   parseJSON val =
       case fromJSON (JSON (Aeson.encode val)) of
-        Left failure -> Aeson.parseFail failure
+        Left failure -> Aeson.parseFail (show failure)
         Right tx     -> return $ UseExternalJSON tx
 
diff --git a/src/Foreign/Rust/Marshall/Variable.hs b/src/Foreign/Rust/Marshall/Variable.hs
index 573e0fc..84a69e7 100644
--- a/src/Foreign/Rust/Marshall/Variable.hs
+++ b/src/Foreign/Rust/Marshall/Variable.hs
@@ -11,26 +11,20 @@ module Foreign.Rust.Marshall.Variable (
   , Buffer -- opaque
   , getVarBuffer
   , withBorshVarBuffer
-  , withBorshFailure
   , withBorshBufferOfInitSize
     -- ** Pure variants
   , withPureBorshVarBuffer
-  , withPureBorshFailure
   ) where
 
 import Codec.Borsh
-import Data.Bifunctor
-import Data.Text (Text)
 import Data.Typeable
 import Foreign
 import Foreign.C.Types
-import GHC.Stack
 import System.IO.Unsafe (unsafePerformIO)
 
 import qualified Data.ByteString as Strict
 
 import Foreign.Rust.Marshall.Util
-import Foreign.Rust.Failure
 
 {-------------------------------------------------------------------------------
   Haskell to Rust
@@ -72,16 +66,6 @@ withBorshVarBuffer :: forall a.
   => (Buffer a -> IO ()) -> IO a
 withBorshVarBuffer = withBorshBufferOfInitSize 1024
 
--- | Wrapper around 'withBorshVarBuffer' with explicit support for failures
-withBorshFailure :: forall a.
-     ( FromBorsh a
-     , StaticBorshSize a ~ 'HasVariableSize
-     , Typeable a
-     , HasCallStack
-     )
-  => (Buffer (Either Text a) -> IO ()) -> IO (Either Failure a)
-withBorshFailure = fmap (first mkFailure) . withBorshVarBuffer
-
 {-------------------------------------------------------------------------------
   Pure variants
 -------------------------------------------------------------------------------}
@@ -94,15 +78,6 @@ withPureBorshVarBuffer :: forall a.
   => (Buffer a -> IO ()) -> a
 withPureBorshVarBuffer = unsafePerformIO . withBorshVarBuffer
 
-withPureBorshFailure :: forall a.
-     ( FromBorsh a
-     , StaticBorshSize a ~ 'HasVariableSize
-     , Typeable a
-     , HasCallStack
-     )
-  => (Buffer (Either Text a) -> IO ()) -> Either Failure a
-withPureBorshFailure = unsafePerformIO . withBorshFailure
-
 {-------------------------------------------------------------------------------
   Generalization
 -------------------------------------------------------------------------------}