diff --git a/Yesod/Core/Types.hs b/Yesod/Core/Types.hs
--- a/Yesod/Core/Types.hs
+++ b/Yesod/Core/Types.hs
@@ -68,6 +68,9 @@
 import           Control.Monad.Reader               (MonadReader (..))
 import Prelude hiding (catch)
 import Control.DeepSeq (NFData (rnf))
+#if MIN_VERSION_conduit(1, 1, 0)
+import Data.Conduit.Lazy (MonadActive, monadActive)
+#endif
 
 -- Sessions
 type SessionMap = Map Text ByteString
@@ -457,6 +460,13 @@
 instance MonadIO m => MonadLogger (WidgetT site m) where
     monadLoggerLog a b c d = WidgetT $ \hd ->
         liftIO $ fmap (, mempty) $ rheLog (handlerEnv hd) a b c (toLogStr d)
+
+#if MIN_VERSION_conduit(1, 1, 0)
+instance MonadActive m => MonadActive (WidgetT site m) where
+    monadActive = lift monadActive
+instance MonadActive m => MonadActive (HandlerT site m) where
+    monadActive = lift monadActive
+#endif
 
 instance MonadTrans (HandlerT site) where
     lift = HandlerT . const
diff --git a/yesod-core.cabal b/yesod-core.cabal
--- a/yesod-core.cabal
+++ b/yesod-core.cabal
@@ -1,5 +1,5 @@
 name:            yesod-core
-version:         1.2.18
+version:         1.2.19
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>