diff --git a/Distribution/Verbosity.hs b/Distribution/Verbosity.hs
index d03d81222a9d09fd75d776ae95b39acc54a00724..2455332c6ecbb068bf07c1b022a2b023962c7045 100644
--- a/Distribution/Verbosity.hs
+++ b/Distribution/Verbosity.hs
@@ -98,7 +98,8 @@ flagToVerbosity (Just s)
        [(i, "")] ->
            case intToVerbosity i of
                Just v -> v
-               Nothing -> error ("Bad verbosity " ++ show i)
+               Nothing -> error ("Bad verbosity: " ++ show i ++
+                                 ". Valid values are 0..3")
        _ -> error ("Can't parse verbosity " ++ s)
 
 showForCabal, showForGHC :: Verbosity -> String