diff --git a/Distribution/Compat/Exception.hs b/Distribution/Compat/Exception.hs
index d275a5fa214a3fce05e329fd6e2372151f3bc3d5..fe5600966a2f6c21ea103dff47908008b484823b 100644
--- a/Distribution/Compat/Exception.hs
+++ b/Distribution/Compat/Exception.hs
@@ -16,7 +16,7 @@ module Distribution.Compat.Exception
 import System.Exit
 import qualified Control.Exception as Exception
 
-onException :: IO a -> IO () -> IO a
+onException :: IO a -> IO b -> IO a
 #ifdef NEW_EXCEPTION
 onException = Exception.onException
 #else