diff -ru orig/Setup.lhs new/Setup.lhs
--- orig/Setup.lhs	2013-10-10 10:21:21.877692795 +0300
+++ new/Setup.lhs	2013-10-10 10:21:21.000000000 +0300
@@ -2,6 +2,7 @@
 
 \begin{code}
 {- OPTIONS_GHC -Wall #-}
+{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
 
 import Control.Monad (liftM2, mplus)
 import Data.List (isPrefixOf)
@@ -22,8 +23,19 @@
     }
 }
 
+-- 'ConstOrId' is a Cabal compatibility hack.
+-- see: https://github.com/scrive/hdbc-postgresql/commit/e9b2fbab07b8f55ae6a9e120ab0b98c433842a8b
+class ConstOrId a b where
+    constOrId :: a -> b
+
+instance ConstOrId a a where
+    constOrId = id
+
+instance ConstOrId a (b -> a) where
+    constOrId = const
+
 mysqlConfigProgram = (simpleProgram "mysql_config") {
-    programFindLocation = \verbosity -> liftM2 mplus
+    programFindLocation = \verbosity -> constOrId $ liftM2 mplus
       (findProgramLocation verbosity "mysql_config")
       (findProgramLocation verbosity "mysql_config5")
   }