diff --git a/Data/Encoding/ASCII.hs b/Data/Encoding/ASCII.hs
index 990ae2d..e261df1 100644
--- a/Data/Encoding/ASCII.hs
+++ b/Data/Encoding/ASCII.hs
@@ -1,10 +1,12 @@
 {-# LANGUAGE DeriveDataTypeable #-}
 module Data.Encoding.ASCII where
 
+import Control.Throws
 import Data.Char
 import Data.Encoding.Base
 import Data.Encoding.ByteSource
 import Data.Encoding.ByteSink
+import Data.Encoding.Exception
 import Data.Typeable
 
 data ASCII = ASCII deriving (Show,Eq,Typeable)
@@ -13,6 +15,7 @@ instance Encoding ASCII where
     decodeChar _ = do
       w <- fetchWord8
       return $ chr $ fromIntegral w
-    encodeChar _ c = do
-      pushWord8 $ fromIntegral $ ord c
+    encodeChar enc c
+      | encodeable enc c = pushWord8 . fromIntegral . ord $ c
+      | otherwise        = throwException . HasNoRepresentation $ c
     encodeable _ c = c < '\128'
\ No newline at end of file