diff --git a/Data/HashMap/Base.hs b/Data/HashMap/Internal.hs
similarity index 99%
rename from Data/HashMap/Base.hs
rename to Data/HashMap/Internal.hs
index 395c5fd9..656dc14c 100644
--- a/Data/HashMap/Base.hs
+++ b/Data/HashMap/Internal.hs
@@ -11,7 +11,19 @@
 #endif
 {-# OPTIONS_GHC -fno-full-laziness -funbox-strict-fields #-}
 
-module Data.HashMap.Base
+-- | = WARNING
+--
+-- This module is considered __internal__.
+--
+-- The Package Versioning Policy __does not apply__.
+--
+-- The contents of this module may change __in any way whatsoever__
+-- and __without any warning__ between minor versions of this package.
+--
+-- Authors importing this module are expected to track development
+-- closely.
+
+module Data.HashMap.Internal
     (
       HashMap(..)
     , Leaf(..)
@@ -140,11 +152,11 @@ import GHC.Exts ((==#), build, reallyUnsafePtrEquality#)
 import Prelude hiding (filter, foldl, foldr, lookup, map, null, pred)
 import Text.Read hiding (step)
 
-import qualified Data.HashMap.Array as A
+import qualified Data.HashMap.Internal.Array as A
 import qualified Data.Hashable as H
 import Data.Hashable (Hashable)
-import Data.HashMap.Unsafe (runST)
-import Data.HashMap.List (isPermutationBy, unorderedCompare)
+import Data.HashMap.Internal.Unsafe (runST)
+import Data.HashMap.Internal.List (isPermutationBy, unorderedCompare)
 import Data.Typeable (Typeable)
 
 import GHC.Exts (isTrue#)
@@ -283,7 +295,7 @@ fromListConstr :: Constr
 fromListConstr = mkConstr hashMapDataType "fromList" [] Prefix
 
 hashMapDataType :: DataType
-hashMapDataType = mkDataType "Data.HashMap.Base.HashMap" [fromListConstr]
+hashMapDataType = mkDataType "Data.HashMap.Internal.HashMap" [fromListConstr]
 
 type Hash   = Word
 type Bitmap = Word
@@ -729,7 +741,7 @@ lookupDefault def k t = findWithDefault def k t
 #endif
 (!) m k = case lookup k m of
     Just v  -> v
-    Nothing -> error "Data.HashMap.Base.(!): key not found"
+    Nothing -> error "Data.HashMap.Internal.(!): key not found"
 {-# INLINABLE (!) #-}
 
 infixl 9 !
diff --git a/Data/HashMap/Array.hs b/Data/HashMap/Internal/Array.hs
similarity index 95%
rename from Data/HashMap/Array.hs
rename to Data/HashMap/Internal/Array.hs
index 8dc23e9e..d1a5307f 100644
--- a/Data/HashMap/Array.hs
+++ b/Data/HashMap/Internal/Array.hs
@@ -1,10 +1,24 @@
 {-# LANGUAGE BangPatterns, CPP, MagicHash, Rank2Types, UnboxedTuples, ScopedTypeVariables #-}
 {-# OPTIONS_GHC -fno-full-laziness -funbox-strict-fields #-}
 
--- | Zero based arrays.
+-- | = WARNING
+--
+-- This module is considered __internal__.
+--
+-- The Package Versioning Policy __does not apply__.
+--
+-- The contents of this module may change __in any way whatsoever__
+-- and __without any warning__ between minor versions of this package.
+--
+-- Authors importing this module are expected to track development
+-- closely.
+--
+-- = Description
+--
+-- Zero based arrays.
 --
 -- Note that no bounds checking are performed.
-module Data.HashMap.Array
+module Data.HashMap.Internal.Array
     ( Array
     , MArray
 
@@ -88,7 +102,7 @@ import Data.Monoid (Monoid (..))
 import qualified Prelude
 #endif
 
-import Data.HashMap.Unsafe (runST)
+import Data.HashMap.Internal.Unsafe (runST)
 import Control.Monad ((>=>))
 
 
@@ -163,9 +177,9 @@ copyMutableArray# = copySmallMutableArray#
 -- This fugly hack is brought by GHC's apparent reluctance to deal
 -- with MagicHash and UnboxedTuples when inferring types. Eek!
 # define CHECK_BOUNDS(_func_,_len_,_k_) \
-if (_k_) < 0 || (_k_) >= (_len_) then error ("Data.HashMap.Array." ++ (_func_) ++ ": bounds error, offset " ++ show (_k_) ++ ", length " ++ show (_len_)) else
+if (_k_) < 0 || (_k_) >= (_len_) then error ("Data.HashMap.Internal.Array." ++ (_func_) ++ ": bounds error, offset " ++ show (_k_) ++ ", length " ++ show (_len_)) else
 # define CHECK_OP(_func_,_op_,_lhs_,_rhs_) \
-if not ((_lhs_) _op_ (_rhs_)) then error ("Data.HashMap.Array." ++ (_func_) ++ ": Check failed: _lhs_ _op_ _rhs_ (" ++ show (_lhs_) ++ " vs. " ++ show (_rhs_) ++ ")") else
+if not ((_lhs_) _op_ (_rhs_)) then error ("Data.HashMap.Internal.Array." ++ (_func_) ++ ": Check failed: _lhs_ _op_ _rhs_ (" ++ show (_lhs_) ++ " vs. " ++ show (_rhs_) ++ ")") else
 # define CHECK_GT(_func_,_lhs_,_rhs_) CHECK_OP(_func_,>,_lhs_,_rhs_)
 # define CHECK_LE(_func_,_lhs_,_rhs_) CHECK_OP(_func_,<=,_lhs_,_rhs_)
 # define CHECK_EQ(_func_,_lhs_,_rhs_) CHECK_OP(_func_,==,_lhs_,_rhs_)
@@ -448,7 +462,7 @@ foldMap f = \ary0 -> case length ary0 of
 {-# INLINE foldMap #-}
 
 undefinedElem :: a
-undefinedElem = error "Data.HashMap.Array: Undefined element"
+undefinedElem = error "Data.HashMap.Internal.Array: Undefined element"
 {-# NOINLINE undefinedElem #-}
 
 thaw :: Array e -> Int -> Int -> ST s (MArray s e)
diff --git a/Data/HashMap/List.hs b/Data/HashMap/Internal/List.hs
similarity index 82%
rename from Data/HashMap/List.hs
rename to Data/HashMap/Internal/List.hs
index c0f55aa0..cb4cfcbd 100644
--- a/Data/HashMap/List.hs
+++ b/Data/HashMap/Internal/List.hs
@@ -1,9 +1,24 @@
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# OPTIONS_GHC -fno-full-laziness -funbox-strict-fields #-}
--- | Extra list functions
+
+-- | = WARNING
+--
+-- This module is considered __internal__.
+--
+-- The Package Versioning Policy __does not apply__.
+--
+-- The contents of this module may change __in any way whatsoever__
+-- and __without any warning__ between minor versions of this package.
+--
+-- Authors importing this module are expected to track development
+-- closely.
+--
+-- = Description
+--
+-- Extra list functions
 --
 -- In separate module to aid testing.
-module Data.HashMap.List
+module Data.HashMap.Internal.List
     ( isPermutationBy
     , deleteBy
     , unorderedCompare
diff --git a/Data/HashMap/Strict/Base.hs b/Data/HashMap/Internal/Strict.hs
similarity index 97%
rename from Data/HashMap/Strict/Base.hs
rename to Data/HashMap/Internal/Strict.hs
index 48dced5e..971ebd7e 100644
--- a/Data/HashMap/Strict/Base.hs
+++ b/Data/HashMap/Internal/Strict.hs
@@ -8,9 +8,22 @@
 -- Copyright   :  2010-2012 Johan Tibell
 -- License     :  BSD-style
 -- Maintainer  :  johan.tibell@gmail.com
--- Stability   :  provisional
 -- Portability :  portable
 --
+-- = WARNING
+--
+-- This module is considered __internal__.
+--
+-- The Package Versioning Policy __does not apply__.
+--
+-- The contents of this module may change __in any way whatsoever__
+-- and __without any warning__ between minor versions of this package.
+--
+-- Authors importing this module are expected to track development
+-- closely.
+--
+-- = Description
+--
 -- A map from /hashable/ keys to values.  A map cannot contain
 -- duplicate keys; each key can map to at most one value.  A 'HashMap'
 -- makes no guarantees as to the order of its elements.
@@ -23,7 +36,7 @@
 -- Many operations have a average-case complexity of /O(log n)/.  The
 -- implementation uses a large base (i.e. 16) so in practice these
 -- operations are constant time.
-module Data.HashMap.Strict.Base
+module Data.HashMap.Internal.Strict
     (
       -- * Strictness properties
       -- $strictness
@@ -107,15 +120,15 @@ import qualified Data.List as L
 import Data.Hashable (Hashable)
 import Prelude hiding (map, lookup)
 
-import qualified Data.HashMap.Array as A
-import qualified Data.HashMap.Base as HM
-import Data.HashMap.Base hiding (
+import qualified Data.HashMap.Internal.Array as A
+import qualified Data.HashMap.Internal as HM
+import Data.HashMap.Internal hiding (
     alter, alterF, adjust, fromList, fromListWith, fromListWithKey,
     insert, insertWith,
     differenceWith, intersectionWith, intersectionWithKey, map, mapWithKey,
     mapMaybe, mapMaybeWithKey, singleton, update, unionWith, unionWithKey,
     traverseWithKey)
-import Data.HashMap.Unsafe (runST)
+import Data.HashMap.Internal.Unsafe (runST)
 #if MIN_VERSION_base(4,8,0)
 import Data.Functor.Identity
 #endif
@@ -310,7 +323,7 @@ alterF f = \ !k !m ->
 {-# INLINABLE [0] alterF #-}
 
 #if MIN_VERSION_base(4,8,0)
--- See notes in Data.HashMap.Base
+-- See notes in Data.HashMap.Internal
 test_bottom :: a
 test_bottom = error "Data.HashMap.alterF internal error: hit test_bottom"
 
@@ -322,7 +335,7 @@ impossibleAdjust = error "Data.HashMap.alterF internal error: impossible adjust"
 
 {-# RULES
 
--- See detailed notes on alterF rules in Data.HashMap.Base.
+-- See detailed notes on alterF rules in Data.HashMap.Internal.
 
 "alterFWeird" forall f. alterF f =
     alterFWeird (f Nothing) (f (Just test_bottom)) f
diff --git a/Data/HashMap/Unsafe.hs b/Data/HashMap/Internal/Unsafe.hs
similarity index 69%
rename from Data/HashMap/Unsafe.hs
rename to Data/HashMap/Internal/Unsafe.hs
index 382d5dbf..ae56c9a6 100644
--- a/Data/HashMap/Unsafe.hs
+++ b/Data/HashMap/Internal/Unsafe.hs
@@ -4,7 +4,21 @@
 {-# LANGUAGE MagicHash, Rank2Types, UnboxedTuples #-}
 #endif
 
--- | This module exports a workaround for this bug:
+-- | = WARNING
+--
+-- This module is considered __internal__.
+--
+-- The Package Versioning Policy __does not apply__.
+--
+-- The contents of this module may change __in any way whatsoever__
+-- and __without any warning__ between minor versions of this package.
+--
+-- Authors importing this module are expected to track development
+-- closely.
+--
+-- = Description
+--
+-- This module exports a workaround for this bug:
 --
 --    http://hackage.haskell.org/trac/ghc/ticket/5916
 --
@@ -12,7 +26,7 @@
 -- understand what's going on here.
 --
 -- Code that uses this module should be compiled with -fno-full-laziness
-module Data.HashMap.Unsafe
+module Data.HashMap.Internal.Unsafe
     ( runST
     ) where
 
diff --git a/Data/HashMap/Lazy.hs b/Data/HashMap/Lazy.hs
index 8252c6d3..64ccde3d 100644
--- a/Data/HashMap/Lazy.hs
+++ b/Data/HashMap/Lazy.hs
@@ -100,8 +100,8 @@ module Data.HashMap.Lazy
     , HS.keysSet
     ) where
 
-import Data.HashMap.Base as HM
-import qualified Data.HashSet.Base as HS
+import Data.HashMap.Internal as HM
+import qualified Data.HashSet.Internal as HS
 import Prelude ()
 
 -- $strictness
diff --git a/Data/HashMap/Strict.hs b/Data/HashMap/Strict.hs
index e94f8464..72e5d11f 100644
--- a/Data/HashMap/Strict.hs
+++ b/Data/HashMap/Strict.hs
@@ -99,8 +99,8 @@ module Data.HashMap.Strict
     , HS.keysSet
     ) where
 
-import Data.HashMap.Strict.Base as HM
-import qualified Data.HashSet.Base as HS
+import Data.HashMap.Internal.Strict as HM
+import qualified Data.HashSet.Internal as HS
 import Prelude ()
 
 -- $strictness
diff --git a/Data/HashSet.hs b/Data/HashSet.hs
index 43d8bba8..ea38c700 100644
--- a/Data/HashSet.hs
+++ b/Data/HashSet.hs
@@ -137,5 +137,5 @@ module Data.HashSet
     , fromMap
     ) where
 
-import Data.HashSet.Base
+import Data.HashSet.Internal
 import Prelude ()
diff --git a/Data/HashSet/Base.hs b/Data/HashSet/Internal.hs
similarity index 95%
rename from Data/HashSet/Base.hs
rename to Data/HashSet/Internal.hs
index fb2bf721..2cf5fd2d 100644
--- a/Data/HashSet/Base.hs
+++ b/Data/HashSet/Internal.hs
@@ -9,13 +9,26 @@
 
 ------------------------------------------------------------------------
 -- |
--- Module      :  Data.HashSet.Base
+-- Module      :  Data.HashSet.Internal
 -- Copyright   :  2011 Bryan O'Sullivan
 -- License     :  BSD-style
 -- Maintainer  :  johan.tibell@gmail.com
--- Stability   :  provisional
 -- Portability :  portable
 --
+-- = WARNING
+--
+-- This module is considered __internal__.
+--
+-- The Package Versioning Policy __does not apply__.
+--
+-- The contents of this module may change __in any way whatsoever__
+-- and __without any warning__ between minor versions of this package.
+--
+-- Authors importing this module are expected to track development
+-- closely.
+--
+-- = Description
+--
 -- A set of /hashable/ values.  A set cannot contain duplicate items.
 -- A 'HashSet' makes no guarantees as to the order of its elements.
 --
@@ -28,7 +41,7 @@
 -- implementation uses a large base (i.e. 16) so in practice these
 -- operations are constant time.
 
-module Data.HashSet.Base
+module Data.HashSet.Internal
     (
       HashSet
 
@@ -79,7 +92,7 @@ module Data.HashSet.Base
 
 import Control.DeepSeq (NFData(..))
 import Data.Data hiding (Typeable)
-import Data.HashMap.Base
+import Data.HashMap.Internal
   ( HashMap, foldMapWithKey, foldlWithKey, foldrWithKey
   , equalKeys, equalKeys1)
 import Data.Hashable (Hashable(hashWithSalt))
@@ -91,7 +104,7 @@ import Data.Monoid (Monoid(..))
 import GHC.Exts (build)
 import Prelude hiding (filter, foldr, foldl, map, null)
 import qualified Data.Foldable as Foldable
-import qualified Data.HashMap.Base as H
+import qualified Data.HashMap.Internal as H
 import qualified Data.List as List
 import Data.Typeable (Typeable)
 import Text.Read
@@ -257,7 +270,7 @@ fromListConstr :: Constr
 fromListConstr = mkConstr hashSetDataType "fromList" [] Prefix
 
 hashSetDataType :: DataType
-hashSetDataType = mkDataType "Data.HashSet.Base.HashSet" [fromListConstr]
+hashSetDataType = mkDataType "Data.HashSet.Internal.HashSet" [fromListConstr]
 
 -- | /O(1)/ Construct an empty set.
 --
diff --git a/tests/List.hs b/tests/List.hs
index 2bf8e0b2..f95889df 100644
--- a/tests/List.hs
+++ b/tests/List.hs
@@ -1,6 +1,6 @@
 module Main (main) where
 
-import Data.HashMap.List
+import Data.HashMap.Internal.List
 import Data.List (nub, sort, sortBy)
 import Data.Ord (comparing)
 
@@ -9,7 +9,7 @@ import Test.Framework.Providers.QuickCheck2 (testProperty)
 import Test.QuickCheck ((==>), (===), property, Property)
 
 tests :: Test
-tests = testGroup "Data.HashMap.List"
+tests = testGroup "Data.HashMap.Internal.List"
     [ testProperty "isPermutationBy" pIsPermutation
     , testProperty "isPermutationBy of different length" pIsPermutationDiffLength
     , testProperty "pUnorderedCompare" pUnorderedCompare
diff --git a/unordered-containers.cabal b/unordered-containers.cabal
index aec2a713..e81d8b41 100644
--- a/unordered-containers.cabal
+++ b/unordered-containers.cabal
@@ -37,16 +37,15 @@ flag debug
 
 library
   exposed-modules:
+    Data.HashMap.Internal
+    Data.HashMap.Internal.Array
+    Data.HashMap.Internal.List
+    Data.HashMap.Internal.Strict
+    Data.HashMap.Internal.Unsafe
     Data.HashMap.Lazy
     Data.HashMap.Strict
     Data.HashSet
-  other-modules:
-    Data.HashMap.Array
-    Data.HashMap.Base
-    Data.HashMap.Strict.Base
-    Data.HashMap.List
-    Data.HashMap.Unsafe
-    Data.HashSet.Base
+    Data.HashSet.Internal
 
   build-depends:
     base >= 4.7 && < 5,
@@ -130,7 +129,7 @@ test-suite list-tests
   hs-source-dirs: tests .
   main-is: List.hs
   other-modules:
-    Data.HashMap.List
+    Data.HashMap.Internal.List
   type: exitcode-stdio-1.0
 
   build-depends:
diff --git a/utils/Stats.hs b/utils/Stats.hs
index e0f27020..8b01ecdc 100644
--- a/utils/Stats.hs
+++ b/utils/Stats.hs
@@ -3,9 +3,9 @@
 {-# OPTIONS_GHC -funbox-strict-fields #-}
 module Stats where
 
-import qualified Data.HashMap.Array as A
-import Data.HashMap.Base (HashMap(..))
-import qualified Data.HashMap.Base as HM
+import qualified Data.HashMap.Internal.Array as A
+import Data.HashMap.Internal (HashMap(..))
+import qualified Data.HashMap.Internal as HM
 import Data.Semigroup
 
 data Histogram = H {