diff --git a/Yesod/Definitions.hs b/Yesod/Definitions.hs
index 97243d06..65a726fd 100644
--- a/Yesod/Definitions.hs
+++ b/Yesod/Definitions.hs
@@ -17,6 +17,7 @@ module Yesod.Definitions
     ( Verb (..)
     , toVerb
     , Resource
+    , Approot (..)
     ) where
 
 import qualified Hack
@@ -31,3 +32,8 @@ toVerb Hack.POST = Post
 toVerb _ = Get
 
 type Resource = [String]
+
+-- | An absolute URL to the base of this application. This can almost be done
+-- programatically, but due to ambiguities in different ways of doing URL
+-- rewriting for (fast)cgi applications, it should be supplied by the user.
+newtype Approot = Approot { unApproot :: String }
diff --git a/Yesod/Helpers/Sitemap.hs b/Yesod/Helpers/Sitemap.hs
index bc1455a5..410cde5c 100644
--- a/Yesod/Helpers/Sitemap.hs
+++ b/Yesod/Helpers/Sitemap.hs
@@ -22,6 +22,7 @@ module Yesod.Helpers.Sitemap
     , SitemapChangeFreq (..)
     ) where
 
+import Yesod.Definitions
 import Yesod.Handler
 import Yesod.Response
 import Web.Encodings
@@ -92,7 +93,6 @@ sitemap urls' = do
     urls <- liftIO urls'
     return $ reps $ SitemapResponse req urls
 
-robots :: Handler
-robots = do
-    ar <- approot
+robots :: Approot -> Handler
+robots (Approot ar) = do
     return $ genResponse "text/plain" $ "Sitemap: " ++ ar ++ "sitemap.xml"