diff -ru orig/tasty.cabal new/tasty.cabal
--- orig/tasty.cabal	2013-12-29 08:32:27.917648136 +0200
+++ new/tasty.cabal	2013-12-29 08:32:27.000000000 +0200
@@ -49,7 +49,7 @@
     regex-tdfa >= 1.1.8,
     optparse-applicative >= 0.6,
     deepseq >= 1.3,
-    either >= 4.0
+    either >= 3.4.2
 
   if flag(colors)
     build-depends: ansi-terminal >= 0.6.1