diff -aur xmobar-0.15.old/xmobar.cabal xmobar-0.15/xmobar.cabal
--- xmobar-0.15.old/xmobar.cabal	2012-06-11 17:04:21.422444926 +0000
+++ xmobar-0.15/xmobar.cabal	2012-06-11 17:05:16.772001865 +0000
@@ -112,7 +112,7 @@
       time,
       filepath,
       X11 == 1.6.*,
-      mtl == 2.0.*,
+      mtl >= 2.0 && <2.2,
       parsec == 3.1.*,
       stm == 2.3.*