diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 0.12.1.0
+
+This release backports some fixes and minor features in the new API.
+
 # 0.12.0.0
 
 * The 0.12.x series is the last major version that will support the old
diff --git a/capnp.cabal b/capnp.cabal
--- a/capnp.cabal
+++ b/capnp.cabal
@@ -1,6 +1,6 @@
 cabal-version:            2.2
 name:                     capnp
-version:                  0.12.0.0
+version:                  0.12.1.0
 category:                 Data, Serialization, Network, Rpc
 copyright:                2016-2021 haskell-capnp contributors (see CONTRIBUTORS file).
 author:                   Ian Denhardt
diff --git a/cmd/capnpc-haskell/Trans/NewToHaskell.hs b/cmd/capnpc-haskell/Trans/NewToHaskell.hs
--- a/cmd/capnpc-haskell/Trans/NewToHaskell.hs
+++ b/cmd/capnpc-haskell/Trans/NewToHaskell.hs
@@ -102,7 +102,7 @@
                         _ -> []
                 , derives =
                     case extraTypeInfo of
-                        Just New.EnumTypeInfo {} -> [ "Std_.Eq", "Std_.Show" ]
+                        Just New.EnumTypeInfo {} -> [ "Std_.Eq", "Std_.Show", "Generics.Generic" ]
                         _                        -> []
                 , dataNewtype = False
                 , dataInstance = False
@@ -948,13 +948,19 @@
         , params = map (Name.UnQ . Name.typeVarName) typeParams ++ ["s_"]
         , funDeps = []
         , decls =
-            map (defineIfaceClassMethod thisMod typeName) methods
+            Hs.CdMinimal
+                [ mkMethodName typeName methodName
+                | New.MethodInfo{methodName} <- methods
+                ]
+            : concatMap (defineIfaceClassMethod thisMod typeName) methods
         }
     ]
 defineIfaceClassMethod thisMod typeName New.MethodInfo{methodName, paramType, resultType} =
-    let mkType t = typeToType thisMod (C.CompositeType t) in
-    Hs.CdValueDecl
-        (Name.valueName (Name.mkSub typeName methodName))
+    let mkType t = typeToType thisMod (C.CompositeType t)
+        name = mkMethodName typeName methodName
+    in
+    [ Hs.CdValueDecl
+        name
         (Hs.TFn
             [ Hs.TVar "s_"
             , Hs.TApp
@@ -964,6 +970,15 @@
                 ]
             ]
         )
+    , Hs.CdValueDef Hs.DfValue
+        { name
+        , params = [Hs.PVar "_"]
+        , value = egName ["GH"] "methodUnimplemented"
+        }
+    ]
+
+mkMethodName typeName methodName =
+    Name.valueName (Name.mkSub typeName methodName)
 
 emitMarshalField :: Name.UnQ -> C.FieldLocType New.Brand Name.CapnpQ -> Hs.Exp
 emitMarshalField name (C.HereField _) =
diff --git a/examples/gen/lib/Capnp/Gen/Calculator/New.hs b/examples/gen/lib/Capnp/Gen/Calculator/New.hs
--- a/examples/gen/lib/Capnp/Gen/Calculator/New.hs
+++ b/examples/gen/lib/Capnp/Gen/Calculator/New.hs
@@ -45,9 +45,13 @@
                                                                             ,(GH.toUntypedMethodHandler ((calculator'defFunction) s_))
                                                                             ,(GH.toUntypedMethodHandler ((calculator'getOperator) s_))] [])
 class (Calculator'server_ s_) where
+    {-# MINIMAL calculator'evaluate,calculator'defFunction,calculator'getOperator #-}
     calculator'evaluate :: s_ -> (GH.MethodHandler Calculator'evaluate'params Calculator'evaluate'results)
+    calculator'evaluate _ = GH.methodUnimplemented
     calculator'defFunction :: s_ -> (GH.MethodHandler Calculator'defFunction'params Calculator'defFunction'results)
+    calculator'defFunction _ = GH.methodUnimplemented
     calculator'getOperator :: s_ -> (GH.MethodHandler Calculator'getOperator'params Calculator'getOperator'results)
+    calculator'getOperator _ = GH.methodUnimplemented
 instance (GH.HasMethod "evaluate" Calculator Calculator'evaluate'params Calculator'evaluate'results) where
     methodByLabel  = (GH.Method 10923537602090224694 0)
 instance (GH.HasMethod "defFunction" Calculator Calculator'defFunction'params Calculator'defFunction'results) where
@@ -379,7 +383,9 @@
     type Server Value = Value'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(Value)) [(GH.toUntypedMethodHandler ((value'read) s_))] [])
 class (Value'server_ s_) where
+    {-# MINIMAL value'read #-}
     value'read :: s_ -> (GH.MethodHandler Value'read'params Value'read'results)
+    value'read _ = GH.methodUnimplemented
 instance (GH.HasMethod "read" Value Value'read'params Value'read'results) where
     methodByLabel  = (GH.Method 14116142932258867410 0)
 data Value'read'params 
@@ -448,7 +454,9 @@
     type Server Function = Function'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(Function)) [(GH.toUntypedMethodHandler ((function'call) s_))] [])
 class (Function'server_ s_) where
+    {-# MINIMAL function'call #-}
     function'call :: s_ -> (GH.MethodHandler Function'call'params Function'call'results)
+    function'call _ = GH.methodUnimplemented
 instance (GH.HasMethod "call" Function Function'call'params Function'call'results) where
     methodByLabel  = (GH.Method 17143016017778443156 0)
 data Function'call'params 
@@ -517,7 +525,9 @@
     | Operator'multiply 
     | Operator'divide 
     | Operator'unknown' Std_.Word16
-    deriving(Std_.Eq,Std_.Show)
+    deriving(Std_.Eq
+            ,Std_.Show
+            ,Generics.Generic)
 type instance (R.ReprFor Operator) = (R.Data R.Sz16)
 instance (C.HasTypeId Operator) where
     typeId  = 9769222902479511526
diff --git a/examples/gen/lib/Capnp/Gen/Echo/New.hs b/examples/gen/lib/Capnp/Gen/Echo/New.hs
--- a/examples/gen/lib/Capnp/Gen/Echo/New.hs
+++ b/examples/gen/lib/Capnp/Gen/Echo/New.hs
@@ -43,7 +43,9 @@
     type Server Echo = Echo'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(Echo)) [(GH.toUntypedMethodHandler ((echo'echo) s_))] [])
 class (Echo'server_ s_) where
+    {-# MINIMAL echo'echo #-}
     echo'echo :: s_ -> (GH.MethodHandler Echo'echo'params Echo'echo'results)
+    echo'echo _ = GH.methodUnimplemented
 instance (GH.HasMethod "echo" Echo Echo'echo'params Echo'echo'results) where
     methodByLabel  = (GH.Method 16940812395455687611 0)
 data Echo'echo'params 
diff --git a/gen/lib/Capnp/Gen/Capnp/Persistent/New.hs b/gen/lib/Capnp/Gen/Capnp/Persistent/New.hs
--- a/gen/lib/Capnp/Gen/Capnp/Persistent/New.hs
+++ b/gen/lib/Capnp/Gen/Capnp/Persistent/New.hs
@@ -45,7 +45,9 @@
     type Server (Persistent sturdyRef owner) = (Persistent'server_ sturdyRef owner)
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @((Persistent sturdyRef owner))) [(GH.toUntypedMethodHandler ((persistent'save @(sturdyRef) @(owner)) s_))] [])
 class (Persistent'server_ sturdyRef owner s_) where
+    {-# MINIMAL persistent'save #-}
     persistent'save :: s_ -> (GH.MethodHandler (Persistent'SaveParams sturdyRef owner) (Persistent'SaveResults sturdyRef owner))
+    persistent'save _ = GH.methodUnimplemented
 instance ((GH.TypeParam sturdyRef)
          ,(GH.TypeParam owner)) => (GH.HasMethod "save" (Persistent sturdyRef owner) (Persistent'SaveParams sturdyRef owner) (Persistent'SaveResults sturdyRef owner)) where
     methodByLabel  = (GH.Method 14468694717054801553 0)
@@ -147,8 +149,11 @@
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @((RealmGateway internalRef externalRef internalOwner externalOwner))) [(GH.toUntypedMethodHandler ((realmGateway'import_ @(internalRef) @(externalRef) @(internalOwner) @(externalOwner)) s_))
                                                                                                                                     ,(GH.toUntypedMethodHandler ((realmGateway'export @(internalRef) @(externalRef) @(internalOwner) @(externalOwner)) s_))] [])
 class (RealmGateway'server_ internalRef externalRef internalOwner externalOwner s_) where
+    {-# MINIMAL realmGateway'import_,realmGateway'export #-}
     realmGateway'import_ :: s_ -> (GH.MethodHandler (RealmGateway'import'params internalRef externalRef internalOwner externalOwner) (Persistent'SaveResults internalRef internalOwner))
+    realmGateway'import_ _ = GH.methodUnimplemented
     realmGateway'export :: s_ -> (GH.MethodHandler (RealmGateway'export'params internalRef externalRef internalOwner externalOwner) (Persistent'SaveResults externalRef externalOwner))
+    realmGateway'export _ = GH.methodUnimplemented
 instance ((GH.TypeParam internalRef)
          ,(GH.TypeParam externalRef)
          ,(GH.TypeParam internalOwner)
diff --git a/gen/lib/Capnp/Gen/Capnp/Rpc/New.hs b/gen/lib/Capnp/Gen/Capnp/Rpc/New.hs
--- a/gen/lib/Capnp/Gen/Capnp/Rpc/New.hs
+++ b/gen/lib/Capnp/Gen/Capnp/Rpc/New.hs
@@ -1332,7 +1332,9 @@
     | Exception'Type'disconnected 
     | Exception'Type'unimplemented 
     | Exception'Type'unknown' Std_.Word16
-    deriving(Std_.Eq,Std_.Show)
+    deriving(Std_.Eq
+            ,Std_.Show
+            ,Generics.Generic)
 type instance (R.ReprFor Exception'Type) = (R.Data R.Sz16)
 instance (C.HasTypeId Exception'Type) where
     typeId  = 12865824133959433560
diff --git a/gen/lib/Capnp/Gen/Capnp/RpcTwoparty/New.hs b/gen/lib/Capnp/Gen/Capnp/RpcTwoparty/New.hs
--- a/gen/lib/Capnp/Gen/Capnp/RpcTwoparty/New.hs
+++ b/gen/lib/Capnp/Gen/Capnp/RpcTwoparty/New.hs
@@ -36,7 +36,9 @@
     = Side'server 
     | Side'client 
     | Side'unknown' Std_.Word16
-    deriving(Std_.Eq,Std_.Show)
+    deriving(Std_.Eq
+            ,Std_.Show
+            ,Generics.Generic)
 type instance (R.ReprFor Side) = (R.Data R.Sz16)
 instance (C.HasTypeId Side) where
     typeId  = 11517567629614739868
diff --git a/gen/lib/Capnp/Gen/Capnp/Schema/New.hs b/gen/lib/Capnp/Gen/Capnp/Schema/New.hs
--- a/gen/lib/Capnp/Gen/Capnp/Schema/New.hs
+++ b/gen/lib/Capnp/Gen/Capnp/Schema/New.hs
@@ -2081,7 +2081,9 @@
     | ElementSize'pointer 
     | ElementSize'inlineComposite 
     | ElementSize'unknown' Std_.Word16
-    deriving(Std_.Eq,Std_.Show)
+    deriving(Std_.Eq
+            ,Std_.Show
+            ,Generics.Generic)
 type instance (R.ReprFor ElementSize) = (R.Data R.Sz16)
 instance (C.HasTypeId ElementSize) where
     typeId  = 15102134695616452902
diff --git a/gen/tests/Capnp/Gen/Aircraft/New.hs b/gen/tests/Capnp/Gen/Aircraft/New.hs
--- a/gen/tests/Capnp/Gen/Aircraft/New.hs
+++ b/gen/tests/Capnp/Gen/Aircraft/New.hs
@@ -117,7 +117,9 @@
     | Airport'dfw 
     | Airport'test 
     | Airport'unknown' Std_.Word16
-    deriving(Std_.Eq,Std_.Show)
+    deriving(Std_.Eq
+            ,Std_.Show
+            ,Generics.Generic)
 type instance (R.ReprFor Airport) = (R.Data R.Sz16)
 instance (C.HasTypeId Airport) where
     typeId  = 16527513525367090977
@@ -1897,7 +1899,9 @@
     type Server Echo = Echo'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(Echo)) [(GH.toUntypedMethodHandler ((echo'echo) s_))] [])
 class (Echo'server_ s_) where
+    {-# MINIMAL echo'echo #-}
     echo'echo :: s_ -> (GH.MethodHandler Echo'echo'params Echo'echo'results)
+    echo'echo _ = GH.methodUnimplemented
 instance (GH.HasMethod "echo" Echo Echo'echo'params Echo'echo'results) where
     methodByLabel  = (GH.Method 10255578992688506164 0)
 data Echo'echo'params 
@@ -2161,7 +2165,9 @@
     type Server CallSequence = CallSequence'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(CallSequence)) [(GH.toUntypedMethodHandler ((callSequence'getNumber) s_))] [])
 class (CallSequence'server_ s_) where
+    {-# MINIMAL callSequence'getNumber #-}
     callSequence'getNumber :: s_ -> (GH.MethodHandler CallSequence'getNumber'params CallSequence'getNumber'results)
+    callSequence'getNumber _ = GH.methodUnimplemented
 instance (GH.HasMethod "getNumber" CallSequence CallSequence'getNumber'params CallSequence'getNumber'results) where
     methodByLabel  = (GH.Method 12371070827563042848 0)
 data CallSequence'getNumber'params 
@@ -2230,7 +2236,9 @@
     type Server CounterFactory = CounterFactory'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(CounterFactory)) [(GH.toUntypedMethodHandler ((counterFactory'newCounter) s_))] [])
 class (CounterFactory'server_ s_) where
+    {-# MINIMAL counterFactory'newCounter #-}
     counterFactory'newCounter :: s_ -> (GH.MethodHandler CounterFactory'newCounter'params CounterFactory'newCounter'results)
+    counterFactory'newCounter _ = GH.methodUnimplemented
 instance (GH.HasMethod "newCounter" CounterFactory CounterFactory'newCounter'params CounterFactory'newCounter'results) where
     methodByLabel  = (GH.Method 15610220054254702620 0)
 data CounterFactory'newCounter'params 
@@ -2304,7 +2312,9 @@
     type Server CounterAcceptor = CounterAcceptor'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(CounterAcceptor)) [(GH.toUntypedMethodHandler ((counterAcceptor'accept) s_))] [])
 class (CounterAcceptor'server_ s_) where
+    {-# MINIMAL counterAcceptor'accept #-}
     counterAcceptor'accept :: s_ -> (GH.MethodHandler CounterAcceptor'accept'params CounterAcceptor'accept'results)
+    counterAcceptor'accept _ = GH.methodUnimplemented
 instance (GH.HasMethod "accept" CounterAcceptor CounterAcceptor'accept'params CounterAcceptor'accept'results) where
     methodByLabel  = (GH.Method 14317498215560924065 0)
 data CounterAcceptor'accept'params 
@@ -2373,7 +2383,9 @@
     type Server Top = Top'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(Top)) [(GH.toUntypedMethodHandler ((top'top) s_))] [])
 class (Top'server_ s_) where
+    {-# MINIMAL top'top #-}
     top'top :: s_ -> (GH.MethodHandler Top'top'params Top'top'results)
+    top'top _ = GH.methodUnimplemented
 instance (GH.HasMethod "top" Top Top'top'params Top'top'results) where
     methodByLabel  = (GH.Method 17861645508359101525 0)
 data Top'top'params 
@@ -2437,7 +2449,9 @@
     type Server Left = Left'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(Left)) [(GH.toUntypedMethodHandler ((left'left) s_))] [(GH.methodHandlerTree (GH.Proxy @(Top)) s_)])
 class ((GH.Server Top s_)) => (Left'server_ s_) where
+    {-# MINIMAL left'left #-}
     left'left :: s_ -> (GH.MethodHandler Left'left'params Left'left'results)
+    left'left _ = GH.methodUnimplemented
 instance (C.Super Top Left)
 instance (GH.HasMethod "left" Left Left'left'params Left'left'results) where
     methodByLabel  = (GH.Method 17679152961798450446 0)
@@ -2502,7 +2516,9 @@
     type Server Right = Right'server_
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @(Right)) [(GH.toUntypedMethodHandler ((right'right) s_))] [(GH.methodHandlerTree (GH.Proxy @(Top)) s_)])
 class ((GH.Server Top s_)) => (Right'server_ s_) where
+    {-# MINIMAL right'right #-}
     right'right :: s_ -> (GH.MethodHandler Right'right'params Right'right'results)
+    right'right _ = GH.methodUnimplemented
 instance (C.Super Top Right)
 instance (GH.HasMethod "right" Right Right'right'params Right'right'results) where
     methodByLabel  = (GH.Method 14712639595305348988 0)
@@ -2569,7 +2585,9 @@
                                                                                                                            ,(GH.methodHandlerTree (GH.Proxy @(Right)) s_)])
 class ((GH.Server Left s_)
       ,(GH.Server Right s_)) => (Bottom'server_ s_) where
+    {-# MINIMAL bottom'bottom #-}
     bottom'bottom :: s_ -> (GH.MethodHandler Bottom'bottom'params Bottom'bottom'results)
+    bottom'bottom _ = GH.methodUnimplemented
 instance (C.Super Left Bottom)
 instance (C.Super Right Bottom)
 instance (GH.HasMethod "bottom" Bottom Bottom'bottom'params Bottom'bottom'results) where
diff --git a/gen/tests/Capnp/Gen/Generics/New.hs b/gen/tests/Capnp/Gen/Generics/New.hs
--- a/gen/tests/Capnp/Gen/Generics/New.hs
+++ b/gen/tests/Capnp/Gen/Generics/New.hs
@@ -302,7 +302,9 @@
     type Server (Nested'SomeInterface t) = (Nested'SomeInterface'server_ t)
     methodHandlerTree _ s_ = (GH.MethodHandlerTree (C.typeId @((Nested'SomeInterface t))) [(GH.toUntypedMethodHandler ((nested'SomeInterface'method @(t)) s_))] [])
 class (Nested'SomeInterface'server_ t s_) where
+    {-# MINIMAL nested'SomeInterface'method #-}
     nested'SomeInterface'method :: s_ -> (GH.MethodHandler (Nested'SomeInterface'method'params t) (Nested'SomeInterface'method'results t))
+    nested'SomeInterface'method _ = GH.methodUnimplemented
 instance ((GH.TypeParam t)) => (GH.HasMethod "method" (Nested'SomeInterface t) (Nested'SomeInterface'method'params t) (Nested'SomeInterface'method'results t)) where
     methodByLabel  = (GH.Method 17400383877992806407 0)
 data Nested'SomeInterface'method'params t
diff --git a/lib/Capnp/New/Basics.hs b/lib/Capnp/New/Basics.hs
--- a/lib/Capnp/New/Basics.hs
+++ b/lib/Capnp/New/Basics.hs
@@ -1,5 +1,7 @@
 {-# LANGUAGE DataKinds             #-}
+{-# LANGUAGE DeriveGeneric         #-}
 {-# LANGUAGE EmptyDataDeriving     #-}
+{-# LANGUAGE FlexibleContexts      #-}
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE OverloadedStrings     #-}
@@ -27,13 +29,15 @@
 import qualified Capnp.Repr          as R
 import qualified Capnp.Untyped       as U
 import           Control.Monad       (when)
-import           Control.Monad.Catch (throwM)
+import           Control.Monad.Catch (MonadThrow, throwM)
 import qualified Data.ByteString     as BS
-import           Data.Foldable       (for_)
+import           Data.Default        (Default(..))
+import           Data.Foldable       (foldl', for_)
 import qualified Data.Text           as T
 import qualified Data.Text.Encoding  as TE
 import qualified Data.Vector         as V
 import           Data.Word
+import           GHC.Generics        (Generic)
 import           GHC.Prim            (coerce)
 
 -- | The Cap'n Proto @Text@ type.
@@ -66,7 +70,7 @@
     = PtrStruct (C.Parsed AnyStruct)
     | PtrList (C.Parsed AnyList)
     | PtrCap M.Client
-    deriving(Show, Eq)
+    deriving(Show, Eq, Generic)
 
 instance C.Parse (Maybe AnyPointer) (Maybe (C.Parsed AnyPointer)) where
     parse (R.Raw ptr) = case ptr of
@@ -104,8 +108,24 @@
     { structData :: V.Vector Word64
     , structPtrs :: V.Vector (Maybe (C.Parsed AnyPointer))
     }
-    deriving(Show, Eq)
+    deriving(Show, Generic)
 
+instance Eq (C.Parsed AnyStruct) where
+    -- We define equality specially (rather than just deriving), such that
+    -- slices are padded out with the default values of their elements.
+    (Struct dl pl) == (Struct dr pr) = sectionEq dl dr && sectionEq pl pr
+      where
+        sectionEq :: (Eq a, Default a) => V.Vector a -> V.Vector a -> Bool
+        sectionEq l r = go 0
+          where
+            go i
+                | i >= length = True
+                | otherwise  = indexDef i l == indexDef i r && go (i+1)
+            length = max (V.length l) (V.length r)
+            indexDef i vec
+                | i < V.length vec = vec V.! i
+                | otherwise = def
+
 instance C.Parse AnyStruct (C.Parsed AnyStruct) where
     parse (R.Raw s) = Struct
         <$> V.generateM
@@ -121,8 +141,8 @@
 instance C.EstimateListAlloc AnyStruct (C.Parsed AnyStruct) where
     estimateListAlloc structs =
         let len = V.length structs
-            nWords = maximum $ map (V.length . structData) $ V.toList structs
-            nPtrs = maximum $ map (V.length . structPtrs) $ V.toList structs
+            nWords = foldl' max 0 $ map (V.length . structData) $ V.toList structs
+            nPtrs  = foldl' max 0 $ map (V.length . structPtrs) $ V.toList structs
         in
         (len, (fromIntegral nWords, fromIntegral nPtrs))
 
@@ -153,7 +173,7 @@
     | List16 (ParsedList Word16)
     | List32 (ParsedList Word32)
     | List64 (ParsedList Word64)
-    deriving(Show, Eq)
+    deriving(Show, Eq, Generic)
 
 instance C.Parse AnyList (C.Parsed AnyList) where
     parse (R.Raw list) = case list of
@@ -237,3 +257,15 @@
 instance C.Allocate AnyStruct where
     type AllocHint AnyStruct = (Word16, Word16)
     new (nWords, nPtrs) msg = R.Raw <$> U.allocStruct msg nWords nPtrs
+
+-- | Return the underlying buffer containing the text. This does not include the
+-- null terminator.
+textBuffer :: MonadThrow m => R.Raw mut Text -> m (R.Raw mut Data)
+textBuffer (R.Raw list) = R.Raw <$> U.take (U.length list - 1) list
+
+-- | Convert a 'Text' to a 'BS.ByteString', comprising the raw bytes of the text
+-- (not counting the NUL terminator).
+textBytes :: U.ReadCtx m 'M.Const => R.Raw 'M.Const Text -> m BS.ByteString
+textBytes text = do
+    R.Raw raw <- textBuffer text
+    U.rawBytes raw
diff --git a/lib/Capnp/New/Rpc/Server.hs b/lib/Capnp/New/Rpc/Server.hs
--- a/lib/Capnp/New/Rpc/Server.hs
+++ b/lib/Capnp/New/Rpc/Server.hs
@@ -33,7 +33,8 @@
 import qualified Capnp.New.Classes       as C
 import qualified Capnp.Repr              as R
 import           Capnp.Repr.Methods      (Client(..))
-import           Capnp.Rpc.Errors        (eFailed, eMethodUnimplemented)
+import           Capnp.Rpc.Errors
+    (eFailed, eMethodUnimplemented, wrapException)
 import           Capnp.Rpc.Promise
     (Fulfiller, breakPromise, fulfill, newCallback)
 import qualified Capnp.Rpc.Server        as Legacy
@@ -185,24 +186,26 @@
     ( C.Parse p pp, R.IsStruct p
     , C.Parse r rr, R.IsStruct r
     ) => (pp -> IO rr) -> MethodHandler p r
-handleParsed handler =
-    handleRaw $ \param -> do
-        p <- evalLimitT defaultLimit $ C.parse param
-        r <- handler p
-        -- TODO: Figure out how to add an instance of Thaw for
-        -- Raw so we can skip the (un)wrapping here.
-        struct <- createPure maxBound $ R.fromRaw <$> parsedToRaw r
-        pure (R.Raw struct)
+handleParsed handler param = propagateExceptions $ \f -> do
+    p <- evalLimitT defaultLimit $ C.parse param
+    r <- handler p
+    -- TODO: Figure out how to add an instance of Thaw for
+    -- Raw so we can skip the (un)wrapping here.
+    struct <- createPure maxBound $ R.fromRaw <$> parsedToRaw r
+    fulfill f (R.Raw struct)
 
 -- | Handle a method, working with the raw (unparsed) form of
 -- parameters and results.
 handleRaw
     :: (R.IsStruct p, R.IsStruct r)
     => (R.Raw 'Const p -> IO (R.Raw 'Const r)) -> MethodHandler p r
-handleRaw handler param f = do
-    res <- handler param `withException` breakPromise f
-    fulfill f res
+handleRaw handler param = propagateExceptions $ \f ->
+    handler param >>= fulfill f
 
+-- Helper for handle*; breaks the promise if the handler throws.
+propagateExceptions :: (Fulfiller a -> IO b) -> Fulfiller a -> IO b
+propagateExceptions h f =
+    h f `withException` (breakPromise f . wrapException False)
 
 -- | 'MethodHandler' that always throws unimplemented.
 methodUnimplemented :: MethodHandler p r