diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+3.1.2
+-----
+* Dependency bump
+
 3.1
 ---
 * Added `Chain` mode, which is `Reverse` using a linear tape that doesn't need to be sorted.
diff --git a/ad.cabal b/ad.cabal
--- a/ad.cabal
+++ b/ad.cabal
@@ -1,5 +1,5 @@
 name:         ad
-version:      3.1.1
+version:      3.1.2
 license:      BSD3
 license-File: LICENSE
 copyright:    (c) Edward Kmett 2010-2012,
@@ -91,7 +91,7 @@
     comonad          == 3.0.*,
     containers       >= 0.2 && < 0.6,
     data-reify       >= 0.6 && < 0.7,
-    free             >= 3.0 && <= 3.2,
+    free             >= 3.0 && <= 3.3,
     reflection       >= 1.1.6 && < 1.2,
     tagged           >= 0.4.2.1 && < 0.5,
     template-haskell >= 2.5 && < 2.9
diff --git a/tests/doctests.hs b/tests/doctests.hs
new file mode 100644
--- /dev/null
+++ b/tests/doctests.hs
@@ -0,0 +1,28 @@
+module Main where
+
+import Test.DocTest
+import System.Directory
+import System.FilePath
+import Control.Applicative
+import Control.Monad
+import Data.List
+
+main :: IO ()
+main = getSources >>= \sources -> doctest $
+    "-isrc"
+  : "-idist/build/autogen"
+  : "-optP-include"
+  : "-optPdist/build/autogen/cabal_macros.h"
+  : sources
+
+getSources :: IO [FilePath]
+getSources = filter (isSuffixOf ".hs") <$> go "src"
+  where
+    go dir = do
+      (dirs, files) <- getFilesAndDirectories dir
+      (files ++) . concat <$> mapM go dirs
+
+getFilesAndDirectories :: FilePath -> IO ([FilePath], [FilePath])
+getFilesAndDirectories dir = do
+  c <- map (dir </>) . filter (`notElem` ["..", "."]) <$> getDirectoryContents dir
+  (,) <$> filterM doesDirectoryExist c <*> filterM doesFileExist c