diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -11,9 +11,7 @@
 
 Most important - this Prelude tries to keep things simple.
 This means it just reexports from base and commonly used libraries
-and doesn't invent its own stuff.
-Furthermore the Prelude is not scattered over many files.
-Everything is exported explicitly to improve the quality of the documentation.
+and doesn't invent its own stuff. Furthermore the Prelude is not scattered over many files.
 
 List of design decisions:
 
@@ -21,7 +19,7 @@
 * Conservative extension over the base Prelude
 * Rely only on very common external libraries
 * Avoid writing custom functions
-* Export everything explicitly for good documentation
+* Export everything explicitly to provide a stable interface and for good documentation
 * Export only total functions or provide safe alternatives (Very few exceptions like div etc.)
 * Prefer Text over String, provide ConvertibleStrings
 * Provide Monad transformers
diff --git a/intro.cabal b/intro.cabal
--- a/intro.cabal
+++ b/intro.cabal
@@ -3,7 +3,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           intro
-version:        0.1.0.5
+version:        0.1.0.6
 synopsis:       "Fixed Prelude" - Mostly total and safe, provides Text and Monad transformers
 description:    Intro is a modern Prelude which provides safe alternatives
                 for most of the partial functions and follows other
@@ -15,7 +15,8 @@
                 This means it just reexports from base and commonly used libraries
                 and doesn\'t invent its own stuff.
                 Furthermore the Prelude is not scattered over many files.
-                Everything is exported explicitly to improve the quality of the documentation.
+                Everything is exported explicitly to provide a stable interface
+                and to improve the quality of the documentation.
 category:       Prelude
 stability:      experimental
 homepage:       https://github.com/minad/intro#readme
diff --git a/src/Intro.hs b/src/Intro.hs
--- a/src/Intro.hs
+++ b/src/Intro.hs
@@ -1,8 +1,9 @@
 {-# OPTIONS_HADDOCK show-extensions #-}
-{-# LANGUAGE Safe #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE NoImplicitPrelude #-}
-{-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE Safe #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -24,7 +25,6 @@
 -- This means it just reexports from base and commonly used libraries
 -- and doesn\'t invent its own stuff.
 -- Furthermore the Prelude is not scattered over many files.
--- Everything is exported explicitly to improve the quality of the documentation.
 --
 -- List of design decisions:
 --
@@ -32,7 +32,7 @@
 -- * Conservative extension over the base Prelude
 -- * Rely only on very common external libraries
 -- * Avoid writing custom functions
--- * Export everything explicitly for good documentation
+-- * Export everything explicitly to provide a stable interface and for good documentation
 -- * Export only total functions or provide safe alternatives (Very few exceptions like div etc.)
 -- * Prefer Text over String, provide ConvertibleStrings
 -- * Provide Monad transformers
@@ -474,6 +474,7 @@
 #else
   , Control.Monad.Monad((>>=), fail)
 #endif
+  , Control.Monad.Fix.MonadFix(mfix)
   , (Control.Monad.=<<)
   , (Control.Monad.<=<)
   , (Control.Monad.>=>)
@@ -597,8 +598,8 @@
   -- * Type level
 #if MIN_VERSION_base(4,9,0)
   , Data.Kind.Type
-  , Data.Kind.Constraint
 #endif
+  , Intro.Trustworthy.Constraint
   , Data.Proxy.Proxy(Proxy)
   , Data.Tagged.Tagged(Tagged)
   , Data.Tagged.unTagged
@@ -636,13 +637,14 @@
   , Intro.Trustworthy.traceShowM
 ) where
 
-import Data.Maybe (Maybe, fromMaybe)
-import Data.Function ((.), ($))
 import Control.Monad.Trans (MonadIO(liftIO))
 import Data.ByteString (ByteString)
+import Data.Function ((.), ($))
+import Data.Maybe (Maybe, fromMaybe)
 import Data.Semigroup ((<>))
 import Data.String.Conversions (ConvertibleStrings(convertString))
 import Data.Text (Text)
+import Intro.Trustworthy (HasCallStack)
 import Prelude (String, Char, FilePath, Show)
 import qualified Control.Applicative
 import qualified Control.Category
@@ -650,6 +652,7 @@
 import qualified Control.Monad
 import qualified Control.Monad.Except
 import qualified Control.Monad.Extra
+import qualified Control.Monad.Fix
 import qualified Control.Monad.RWS.CPS
 import qualified Control.Monad.Reader
 import qualified Control.Monad.State.Strict
@@ -712,10 +715,6 @@
 import qualified Control.Monad.Fail
 import qualified Data.Functor.Classes
 import qualified Data.Kind
-import qualified GHC.Stack.Types
-#define HAS_CALL_STACK GHC.Stack.Types.HasCallStack =>
-#else
-#define HAS_CALL_STACK
 #endif
 
 -- | Alias for lazy 'Data.Text.Lazy.Text'
@@ -848,7 +847,7 @@
 {-# INLINE appendFileUtf8 #-}
 
 -- | Throw an undefined error. Use only for debugging.
-undefined :: HAS_CALL_STACK a
+undefined :: HasCallStack => a
 undefined = Prelude.undefined
 {-# WARNING undefined "'undefined' remains in code" #-}
 
@@ -885,8 +884,8 @@
 --
 -- In general, prefer total functions. You can use 'Maybe', 'Data.Either.Either',
 -- 'Control.Monad.Except.ExceptT' or 'Control.Monad.Except.MonadError' for error handling.
-panic :: HAS_CALL_STACK String -> a
-panic msg = Prelude.error $
+panic :: HasCallStack => Text -> a
+panic msg = Prelude.error $ convertString $
   "Panic: " <> msg <> "\n\n" <>
   "Please submit a bug report including the stacktrace\n" <>
   "and a description on how to reproduce the bug."
diff --git a/src/Intro/Trustworthy.hs b/src/Intro/Trustworthy.hs
--- a/src/Intro/Trustworthy.hs
+++ b/src/Intro/Trustworthy.hs
@@ -1,6 +1,8 @@
-{-# LANGUAGE Trustworthy #-}
-{-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE KindSignatures #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE Trustworthy #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -23,6 +25,8 @@
       , fromList
       -- , toList -- provided by Foldable
       )
+  , Constraint
+  , HasCallStack
   , trace
   , traceIO
   , traceM
@@ -44,9 +48,13 @@
 
 #if MIN_VERSION_base(4,9,0)
 import Control.Applicative (Applicative)
+import Data.Kind (Constraint)
+import GHC.Stack (HasCallStack)
 #define APPLICATIVE Applicative
 #else
 import Control.Monad (Monad)
+import GHC.Exts (Constraint)
+type HasCallStack = (() :: GHC.Exts.Constraint)
 #define APPLICATIVE Monad
 #endif