diff --git a/Foundation.hs b/Foundation.hs
index aba8b34..106d55b 100644
--- a/Foundation.hs
+++ b/Foundation.hs
@@ -46,7 +46,10 @@ type Form x = Html -> MForm (HandlerT App IO) (FormResult x, Widget)
 instance Yesod App where
     -- Controls the base of generated URLs. For more information on modifying,
     -- see: https://github.com/yesodweb/yesod/wiki/Overriding-approot
-    approot = ApprootMaster $ appRoot . appSettings
+    approot = ApprootRequest $ \app req ->
+        case appRoot $ appSettings app of
+            Nothing -> getApprootText guessApproot app req
+            Just root -> root
 
     -- Store session data on the client in encrypted cookies,
     -- default session idle timeout is 120 minutes
diff --git a/PROJECTNAME.cabal b/PROJECTNAME.cabal
index 087b0c3..278b74d 100644
--- a/PROJECTNAME.cabal
+++ b/PROJECTNAME.cabal
@@ -49,7 +49,7 @@ library
 
     build-depends: base                          >= 4          && < 5
                  , yesod                         >= 1.4.1      && < 1.5
-                 , yesod-core                    >= 1.4.14     && < 1.5
+                 , yesod-core                    >= 1.4.17     && < 1.5
                  , yesod-auth                    >= 1.4.0      && < 1.5
                  , yesod-static                  >= 1.4.0.3    && < 1.6
                  , yesod-form                    >= 1.4.0      && < 1.5
diff --git a/Settings.hs b/Settings.hs
index f6c652b..01b6117 100644
--- a/Settings.hs
+++ b/Settings.hs
@@ -27,8 +27,9 @@ data AppSettings = AppSettings
     -- ^ Directory from which to serve static files.
     , appDatabaseConf           :: PostgresConf
     -- ^ Configuration settings for accessing the database.
-    , appRoot                   :: Text
-    -- ^ Base for all generated URLs.
+    , appRoot                   :: Maybe Text
+    -- ^ Base for all generated URLs. If @Nothing@, determined
+    -- from the request headers.
     , appHost                   :: HostPreference
     -- ^ Host/interface the server should bind to.
     , appPort                   :: Int
@@ -65,7 +66,7 @@ instance FromJSON AppSettings where
 #endif
         appStaticDir              <- o .: "static-dir"
         appDatabaseConf           <- o .: "database"
-        appRoot                   <- o .: "approot"
+        appRoot                   <- o .:? "approot"
         appHost                   <- fromString <$> o .: "host"
         appPort                   <- o .: "port"
         appIpFromHeader           <- o .: "ip-from-header"
diff --git a/config/settings.yml b/config/settings.yml
index 4994b28..0b44dec 100644
--- a/config/settings.yml
+++ b/config/settings.yml
@@ -4,9 +4,12 @@
 static-dir:     "_env:STATIC_DIR:static"
 host:           "_env:HOST:*4" # any IPv4 host
 port:           "_env:PORT:3000" # NB: The port `yesod devel` uses is distinct from this value. Set the `yesod devel` port from the command line.
-approot:        "_env:APPROOT:http://localhost:3000"
 ip-from-header: "_env:IP_FROM_HEADER:false"
 
+# Default behavior: determine the application root from the request headers.
+# Uncomment to set an explicit approot
+#approot:        "_env:APPROOT:http://localhost:3000"
+
 # Optional values with the following production defaults.
 # In development, they default to the inverse.
 #