diff --git a/Changelog b/Changelog
--- a/Changelog
+++ b/Changelog
@@ -1,3 +1,9 @@
+Changed in version 0.7.5.0:
+   * Add the new function `fallbackCompletion` to combine
+     multiple `CompletionFunc`s
+   * Fix warnings
+   * Bump the lower bound to ghc-8.0
+
 Changed in version 0.7.4.3:
    * Bump upper bounds on base, containers, stm and unix
    * Fix redundant "Category" field in haskeline.cabal
diff --git a/System/Console/Haskeline/Backend/Posix.hsc b/System/Console/Haskeline/Backend/Posix.hsc
--- a/System/Console/Haskeline/Backend/Posix.hsc
+++ b/System/Console/Haskeline/Backend/Posix.hsc
@@ -303,7 +303,7 @@
 
 type PosixT m = ReaderT Handles m
 
-runPosixT :: Monad m => Handles -> PosixT m a -> m a
+runPosixT :: Handles -> PosixT m a -> m a
 runPosixT h = runReaderT' h
 
 fileRunTerm :: Handle -> IO RunTerm
diff --git a/System/Console/Haskeline/Backend/Terminfo.hs b/System/Console/Haskeline/Backend/Terminfo.hs
--- a/System/Console/Haskeline/Backend/Terminfo.hs
+++ b/System/Console/Haskeline/Backend/Terminfo.hs
@@ -1,3 +1,6 @@
+#if __GLASGOW_HASKELL__ <= 802
+{-# OPTIONS_GHC -Wno-redundant-constraints #-}
+#endif
 module System.Console.Haskeline.Backend.Terminfo(
                             Draw(),
                             runTerminfoDraw
@@ -5,7 +8,6 @@
                              where
 
 import System.Console.Terminfo
-import Control.Applicative
 import Control.Monad
 import Data.List(foldl')
 import System.IO
diff --git a/System/Console/Haskeline/Backend/Win32.hsc b/System/Console/Haskeline/Backend/Win32.hsc
--- a/System/Console/Haskeline/Backend/Win32.hsc
+++ b/System/Console/Haskeline/Backend/Win32.hsc
@@ -15,7 +15,6 @@
 import Control.Concurrent hiding (throwTo)
 import Data.Char(isPrint)
 import Data.Maybe(mapMaybe)
-import Control.Applicative
 import Control.Monad
 
 import System.Console.Haskeline.Key
@@ -166,9 +165,6 @@
 data Coord = Coord {coordX, coordY :: Int}
                 deriving Show
 
-#if __GLASGOW_HASKELL__ < 711
-#let alignment t = "%lu", (unsigned long)offsetof(struct {char x__; t (y__); }, y__)
-#endif
 instance Storable Coord where
     sizeOf _ = (#size COORD)
     alignment _ = (#alignment COORD)
diff --git a/System/Console/Haskeline/Completion.hs b/System/Console/Haskeline/Completion.hs
--- a/System/Console/Haskeline/Completion.hs
+++ b/System/Console/Haskeline/Completion.hs
@@ -3,6 +3,7 @@
                             Completion(..),
                             noCompletion,
                             simpleCompletion,
+                            fallbackCompletion,
                             -- * Word completion
                             completeWord,
                             completeWordWithPrev,
@@ -188,3 +189,12 @@
     home <- getHomeDirectory
     return (home </> path)
 fixPath path = return path
+
+-- | If the first completer produces no suggestions, fallback to the second
+-- completer's output.
+fallbackCompletion :: Monad m => CompletionFunc m -> CompletionFunc m -> CompletionFunc m
+fallbackCompletion a b input = do
+    aCompletions <- a input
+    if null (snd aCompletions)
+        then b input
+        else return aCompletions
diff --git a/System/Console/Haskeline/History.hs b/System/Console/Haskeline/History.hs
--- a/System/Console/Haskeline/History.hs
+++ b/System/Console/Haskeline/History.hs
@@ -86,7 +86,7 @@
 addHistory s h = h {histLines = maybeDropLast (stifleAmt h) (s <| (histLines h))}
 
 -- If the sequence is too big, drop the last entry.
-maybeDropLast :: Ord a => Maybe Int -> Seq a -> Seq a
+maybeDropLast :: Maybe Int -> Seq a -> Seq a
 maybeDropLast maxAmt hs
     | rightSize = hs
     | otherwise = case viewr hs of
diff --git a/System/Console/Haskeline/InputT.hs b/System/Console/Haskeline/InputT.hs
--- a/System/Console/Haskeline/InputT.hs
+++ b/System/Console/Haskeline/InputT.hs
@@ -13,8 +13,6 @@
 
 import System.Directory(getHomeDirectory)
 import System.FilePath
-import Control.Applicative
-import Control.Monad (liftM, ap)
 import Control.Monad.Fix
 import System.IO
 import Data.IORef
diff --git a/System/Console/Haskeline/MonadException.hs b/System/Console/Haskeline/MonadException.hs
--- a/System/Console/Haskeline/MonadException.hs
+++ b/System/Console/Haskeline/MonadException.hs
@@ -1,3 +1,4 @@
+{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
 {- | This module redefines some of the functions in "Control.Exception" to
 work for more general monads built on top of 'IO'.
 -}
@@ -28,9 +29,6 @@
 
 import qualified Control.Exception as E
 import Control.Exception (Exception,SomeException)
-#if __GLASGOW_HASKELL__ < 705
-import Prelude hiding (catch)
-#endif
 import Control.Monad(liftM, join)
 import Control.Monad.IO.Class
 import Control.Monad.Trans.Identity
@@ -41,7 +39,6 @@
 import Control.Monad.Trans.Maybe
 import Control.Monad.Trans.RWS
 import Control.Monad.Trans.Writer
-import Data.Monoid
 import Control.Concurrent(ThreadId)
 
 -- This approach is based on that of the monad-control package.
diff --git a/System/Console/Haskeline/Monads.hs b/System/Console/Haskeline/Monads.hs
--- a/System/Console/Haskeline/Monads.hs
+++ b/System/Console/Haskeline/Monads.hs
@@ -29,9 +29,6 @@
 import Control.Monad.Trans.Reader hiding (ask,asks)
 import qualified Control.Monad.Trans.Reader as Reader
 import Data.IORef
-#if __GLASGOW_HASKELL__ < 705
-import Prelude hiding (catch)
-#endif
 
 import System.Console.Haskeline.MonadException
 
@@ -44,7 +41,8 @@
 instance Monad m => MonadReader s (StateT s m) where
     ask = get
 
-instance (MonadReader r m, MonadTrans t, Monad (t m)) => MonadReader r (t m) where
+instance {-# OVERLAPPABLE #-} (MonadReader r m, MonadTrans t, Monad (t m))
+    => MonadReader r (t m) where
     ask = lift ask
 
 asks :: MonadReader r m => (r -> a) -> m a
@@ -67,7 +65,7 @@
     put s'
     return x
 
-runReaderT' :: Monad m => r -> ReaderT r m a -> m a
+runReaderT' :: r -> ReaderT r m a -> m a
 runReaderT' = flip runReaderT
 
 newtype StateT s m a = StateT { getStateTFunc 
@@ -111,7 +109,8 @@
     get = StateT $ \s -> return $ \f -> f s s
     put s = s `seq` StateT $ \_ -> return $ \f -> f () s
 
-instance (MonadState s m, MonadTrans t, Monad (t m)) => MonadState s (t m) where
+instance {-# OVERLAPPABLE #-} (MonadState s m, MonadTrans t, Monad (t m))
+    => MonadState s (t m) where
     get = lift get
     put = lift . put
 
diff --git a/System/Console/Haskeline/RunCommand.hs b/System/Console/Haskeline/RunCommand.hs
--- a/System/Console/Haskeline/RunCommand.hs
+++ b/System/Console/Haskeline/RunCommand.hs
@@ -20,7 +20,7 @@
                     cmds 
 
 runCommandLoop' :: forall m n s a . (Term n, CommandMonad n,
-        MonadState Layout m, MonadReader Prefs n, LineState s)
+        MonadState Layout m, LineState s)
         => (forall b . m b -> n b) -> TermOps -> Prefix -> s -> KeyCommand m s a -> n Event
         -> n a
 runCommandLoop' liftE tops prefix initState cmds getEvent = do
diff --git a/System/Console/Haskeline/Term.hs b/System/Console/Haskeline/Term.hs
--- a/System/Console/Haskeline/Term.hs
+++ b/System/Console/Haskeline/Term.hs
@@ -9,7 +9,7 @@
 import Control.Concurrent
 import Control.Concurrent.STM
 import Data.Word
-import Control.Exception (fromException, AsyncException(..),bracket_)
+import Control.Exception (fromException, AsyncException(..))
 import Data.Typeable
 import System.IO
 import Control.Monad(liftM,when,guard)
@@ -104,7 +104,7 @@
         => CommandMonad m where
     runCompletion :: (String,String) -> m (String,[Completion])
 
-instance (MonadTrans t, CommandMonad m, MonadReader Prefs (t m),
+instance {-# OVERLAPPABLE #-} (MonadTrans t, CommandMonad m, MonadReader Prefs (t m),
         MonadException (t m),
         MonadReader Layout (t m))
             => CommandMonad (t m) where
@@ -160,7 +160,7 @@
 
 -- | Utility function for changing a property of a terminal for the duration of
 -- a computation.
-bracketSet :: (Eq a, MonadException m) => IO a -> (a -> IO ()) -> a -> m b -> m b
+bracketSet :: MonadException m => IO a -> (a -> IO ()) -> a -> m b -> m b
 bracketSet getState set newState f = bracket (liftIO getState)
                             (liftIO . set)
                             (\_ -> liftIO (set newState) >> f)
diff --git a/haskeline.cabal b/haskeline.cabal
--- a/haskeline.cabal
+++ b/haskeline.cabal
@@ -1,6 +1,6 @@
 Name:           haskeline
 Cabal-Version:  >=1.10
-Version:        0.7.4.3
+Version:        0.7.5.0
 Category:       User Interfaces
 License:        BSD3
 License-File:   LICENSE
@@ -42,9 +42,9 @@
     -- We require ghc>=7.4.1 (base>=4.5) to use the base library encodings, even
     -- though it was implemented in earlier releases, due to GHC bug #5436 which
     -- wasn't fixed until 7.4.1
-    Build-depends: base >=4.5 && < 4.13, containers>=0.4 && < 0.7,
+    Build-depends: base >=4.9 && < 4.13, containers>=0.4 && < 0.7,
                    directory>=1.1 && < 1.4, bytestring>=0.9 && < 0.11,
-                   filepath >= 1.2 && < 1.5, transformers >= 0.2 && < 0.6,
+                   filepath >= 1.2 && < 1.5, transformers >= 0.4 && < 0.6,
                    process >= 1.0 && < 1.7, stm >= 2.4 && < 2.6
     Default-Language: Haskell98
     Default-Extensions:
@@ -53,7 +53,7 @@
                 FlexibleContexts, ExistentialQuantification
                 ScopedTypeVariables, GeneralizedNewtypeDeriving
                 StandaloneDeriving
-                MultiParamTypeClasses, OverlappingInstances
+                MultiParamTypeClasses,
                 UndecidableInstances
                 ScopedTypeVariables, CPP, DeriveDataTypeable,
                 PatternGuards