diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -7,6 +7,24 @@
 *de facto* standard Haskell versioning scheme.
 
 
+1.2.1.1
+-------
+
+- **Date**    2017-10-11
+- **Git tag** [concurrency-1.2.1.1][]
+- **Hackage** https://hackage.haskell.org/package/concurrency-1.2.1.1
+
+### Control.Monad.Conc.Class
+
+- The `IO` instance of `MonadConc` now names threads with `GHC.Conc.labelThread`, so thread names
+  now appear in debugging traces of normal execution.
+
+[concurrency-1.2.1.1]: https://github.com/barrucadu/dejafu/releases/tag/concurrency-1.2.1.1
+
+
+---------------------------------------------------------------------------------------------------
+
+
 1.2.1.0
 -------
 
diff --git a/Control/Monad/Conc/Class.hs b/Control/Monad/Conc/Class.hs
--- a/Control/Monad/Conc/Class.hs
+++ b/Control/Monad/Conc/Class.hs
@@ -81,6 +81,7 @@
 import qualified Control.Monad.STM            as IO
 import qualified Data.Atomics                 as IO
 import qualified Data.IORef                   as IO
+import qualified GHC.Conc                     as IO
 
 -- for the transformer instances
 import           Control.Monad.Reader         (ReaderT)
@@ -613,9 +614,14 @@
   fork   = IO.forkIO
   forkOn = IO.forkOn
 
-  forkWithUnmask   = IO.forkIOWithUnmask
-  forkOnWithUnmask = IO.forkOnWithUnmask
+  forkWithUnmaskN n ma = forkWithUnmask $ \umask -> do
+    labelMe n
+    ma umask
 
+  forkOnWithUnmaskN n i ma = forkOnWithUnmask i $ \umask -> do
+    labelMe n
+    ma umask
+
   getNumCapabilities = IO.getNumCapabilities
   setNumCapabilities = IO.setNumCapabilities
   readMVar           = IO.readMVar
@@ -640,6 +646,13 @@
   modifyCRefCAS      = IO.atomicModifyIORefCAS
   atomically         = IO.atomically
   readTVarConc       = IO.readTVarIO
+
+-- | Label the current thread, if the given label is nonempty.
+labelMe :: String -> IO ()
+labelMe "" = pure ()
+labelMe n  = do
+  tid <- myThreadId
+  IO.labelThread tid n
 
 -------------------------------------------------------------------------------
 -- Transformer instances
diff --git a/concurrency.cabal b/concurrency.cabal
--- a/concurrency.cabal
+++ b/concurrency.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                concurrency
-version:             1.2.1.0
+version:             1.2.1.1
 synopsis:            Typeclasses, functions, and data types for concurrency and STM.
 
 description:
@@ -32,7 +32,7 @@
 source-repository this
   type:     git
   location: https://github.com/barrucadu/dejafu.git
-  tag:      concurrency-1.2.1.0
+  tag:      concurrency-1.2.1.1
 
 library
   exposed-modules:     Control.Monad.Conc.Class