diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # ChangeLog for conduit-extra
 
+## 1.3.6
+
+* Add support for `transformers-0.6`
+
 ## 1.3.5
 
 * Add `createSinkClose`
diff --git a/Data/Conduit/Lazy.hs b/Data/Conduit/Lazy.hs
--- a/Data/Conduit/Lazy.hs
+++ b/Data/Conduit/Lazy.hs
@@ -21,9 +21,11 @@
 import Control.Monad.IO.Unlift (MonadIO, liftIO, MonadUnliftIO, withUnliftIO, unliftIO)
 
 import Control.Monad.Trans.Identity ( IdentityT)
+#if !MIN_VERSION_transformers(0,6,0)
+import Control.Monad.Trans.Error    ( ErrorT, Error)
 import Control.Monad.Trans.List     ( ListT    )
+#endif
 import Control.Monad.Trans.Maybe    ( MaybeT   )
-import Control.Monad.Trans.Error    ( ErrorT, Error)
 import Control.Monad.Trans.Reader   ( ReaderT  )
 import Control.Monad.Trans.State    ( StateT   )
 import Control.Monad.Trans.Writer   ( WriterT  )
@@ -100,9 +102,11 @@
 #define GO(T) instance MonadActive m => MonadActive (T m) where monadActive = lift monadActive
 #define GOX(X, T) instance (X, MonadActive m) => MonadActive (T m) where monadActive = lift monadActive
 GO(IdentityT)
+#if !MIN_VERSION_transformers(0,6,0)
+GOX(Error e, ErrorT e)
 GO(ListT)
+#endif
 GO(MaybeT)
-GOX(Error e, ErrorT e)
 GO(ReaderT r)
 GO(StateT s)
 GOX(Monoid w, WriterT w)
diff --git a/Data/Conduit/Process.hs b/Data/Conduit/Process.hs
--- a/Data/Conduit/Process.hs
+++ b/Data/Conduit/Process.hs
@@ -6,6 +6,9 @@
 -- | A full tutorial for this module is available at:
 -- <https://github.com/snoyberg/conduit/blob/master/PROCESS.md>.
 --
+-- Some utilities in this module require the threaded runtime because they use
+-- 'System.Process.waitForProcess' internally.
+--
 -- Note that this is a very thin layer around the @Data.Streaming.Process@ module. In particular, it:
 --
 -- * Provides orphan instances for conduit
@@ -82,6 +85,8 @@
 -- terminated. This behavior is different from 'sourceProcessWithStreams' due
 -- to historical reasons.
 --
+-- Requires the threaded runtime.
+--
 -- Since 1.1.2
 sourceProcessWithConsumer :: MonadIO m
                           => CreateProcess
@@ -97,6 +102,8 @@
 -- | Like @sourceProcessWithConsumer@ but providing the command to be run as
 -- a @String@.
 --
+-- Requires the threaded runtime.
+--
 -- Since 1.1.2
 sourceCmdWithConsumer :: MonadIO m
                       => String                  -- ^command
@@ -120,6 +127,8 @@
 -- IO is required because the streams are run concurrently
 -- using the <https://hackage.haskell.org/package/async async> package
 --
+-- Requires the threaded runtime.
+--
 -- @since 1.1.12
 sourceProcessWithStreams
   :: MonadUnliftIO m
@@ -148,6 +157,8 @@
 -- | Like @sourceProcessWithStreams@ but providing the command to be run as
 -- a @String@.
 --
+-- Requires the threaded runtime.
+--
 -- @since 1.1.12
 sourceCmdWithStreams
   :: MonadUnliftIO m
@@ -160,6 +171,8 @@
 
 -- | Same as 'withCheckedProcess', but kills the child process in the case of
 -- an exception being thrown by the provided callback function.
+--
+-- Requires the threaded runtime.
 --
 -- @since 1.1.11
 withCheckedProcessCleanup
diff --git a/conduit-extra.cabal b/conduit-extra.cabal
--- a/conduit-extra.cabal
+++ b/conduit-extra.cabal
@@ -1,5 +1,6 @@
+Cabal-version:       >=1.10
 Name:                conduit-extra
-Version:             1.3.5
+Version:             1.3.6
 Synopsis:            Batteries included conduit: adapters for common libraries.
 Description:
     The conduit package itself maintains relative small dependencies. The purpose of this package is to collect commonly used utility functions wrapping other library dependencies, without depending on heavier-weight dependencies. The basic idea is that this package should only depend on haskell-platform packages and conduit.
@@ -9,7 +10,6 @@
 Maintainer:          michael@snoyman.com
 Category:            Data, Conduit
 Build-type:          Simple
-Cabal-version:       >=1.8
 Homepage:            http://github.com/snoyberg/conduit
 extra-source-files:
     test/random
@@ -19,6 +19,7 @@
     README.md
 
 Library
+  default-language:    Haskell2010
   Exposed-modules:     Data.Conduit.Attoparsec
                        Data.Conduit.Binary
                        Data.Conduit.ByteString.Builder
@@ -38,7 +39,7 @@
       -- These architectures are able to perform unaligned memory accesses
       cpp-options: -DALLOW_UNALIGNED_ACCESS
 
-  Build-depends:       base                     >= 4.9          && < 5
+  Build-depends:       base                     >= 4.12         && < 5
                      , conduit                  >= 1.3          && < 1.4
 
                      , bytestring               >= 0.10.2
@@ -62,6 +63,7 @@
 
 test-suite test
     hs-source-dirs: test
+    default-language: Haskell2010
     main-is: Spec.hs
     type: exitcode-stdio-1.0
     ghc-options:   -threaded
@@ -73,7 +75,6 @@
 
                    , async
                    , attoparsec
-                   , bytestring-builder
                    , bytestring
                    , exceptions
                    , process
@@ -86,6 +87,7 @@
                    , transformers-base
                    , directory
                    , filepath
+    build-tool-depends: hspec-discover:hspec-discover
     ghc-options:     -Wall
     if os(windows)
         cpp-options: -DWINDOWS
@@ -102,6 +104,7 @@
                      Data.Conduit.ZlibSpec
 
 benchmark blaze
+    default-language: Haskell2010
     type:           exitcode-stdio-1.0
     hs-source-dirs: bench
     build-depends:  base
@@ -109,7 +112,6 @@
                   , conduit-extra
                   , gauge
                   , bytestring
-                  , bytestring-builder
                   , transformers
     main-is:        blaze.hs
     ghc-options:    -Wall -O2 -rtsopts