diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,11 +4,12 @@
 
 The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
-## Unreleased
+## [0.2.1] - 2019-06-17
 
 ### Added
 
-### Changed
+* Compatibility with ghc-8.6.
+* Check for -threaded.
 
 ## [0.2.0] - 2017-11-06
 
diff --git a/pthread.cabal b/pthread.cabal
--- a/pthread.cabal
+++ b/pthread.cabal
@@ -1,5 +1,5 @@
 name:                pthread
-version:             0.2.0
+version:             0.2.1
 synopsis:            Bindings for the pthread library.
 homepage:            http://github.com/tweag/pthread
 license:             BSD3
@@ -25,7 +25,7 @@
   exposed-modules:
     System.Posix.Thread
   build-depends:
-    base > 4.9.0.0 && < 5,
+    base >= 4.9.0.0 && < 5,
     generic-deriving >= 1.11
   default-language: Haskell2010
 
diff --git a/src/System/Posix/Thread.hsc b/src/System/Posix/Thread.hsc
--- a/src/System/Posix/Thread.hsc
+++ b/src/System/Posix/Thread.hsc
@@ -40,6 +40,7 @@
 import Control.Exception (Exception, bracket_, throwIO)
 import Control.Monad (forM_, unless, when)
 import Data.Monoid (First(..))
+import Data.Semigroup (Semigroup(..))
 import Foreign.C.Types
 import Foreign.C.Error (Errno(..), errnoToIOError)
 import Foreign.Marshal.Alloc (alloca)
@@ -67,6 +68,7 @@
 create :: IO (Ptr a) -> IO ThreadId
 create action =
     alloca $ \tidPtr -> do
+      unless rtsSupportsBoundThreads (error "Use -threaded RTS.")
       fptr <- wrap $ \_ -> action
       throwIfNonZero_ $ pthread_create tidPtr nullPtr fptr nullPtr
       peek tidPtr
@@ -88,6 +90,7 @@
 createWithAttributes attrs action =
     alloca $ \tidPtr ->
     alloca $ \attrsPtr -> do
+      unless rtsSupportsBoundThreads (error "Use -threaded RTS.")
       bracket_
         (throwIfNonZero_ $ pthread_attr_init attrsPtr)
         (throwIfNonZero_ $ pthread_attr_destroy attrsPtr) $ do
@@ -223,9 +226,12 @@
   , stackSize :: First CSize
   } deriving (Generic, Show)
 
+instance Semigroup AttributesMonoid where
+  (<>) = mappenddefault
+
 instance Monoid AttributesMonoid where
   mempty = memptydefault
-  mappend = mappenddefault
+  mappend = (<>)
 
 monoidFromAttributes :: Attributes -> AttributesMonoid
 monoidFromAttributes Attributes{..} =