diff --git a/System/Posix/IO.hsc b/System/Posix/IO.hsc
--- a/System/Posix/IO.hsc
+++ b/System/Posix/IO.hsc
@@ -12,7 +12,7 @@
 -- POSIX IO support.  These types and functions correspond to the unix
 -- functions open(2), close(2), etc.  For more portable functions
 -- which are more like fopen(3) and friends from stdio.h, see
--- 'System.IO'.
+-- "System.IO".
 --
 -----------------------------------------------------------------------------
 
diff --git a/System/Posix/Process.hsc b/System/Posix/Process.hsc
--- a/System/Posix/Process.hsc
+++ b/System/Posix/Process.hsc
@@ -9,8 +9,8 @@
 -- Stability   :  provisional
 -- Portability :  non-portable (requires POSIX)
 --
--- POSIX process support.  See also the "System.Cmd" and "System.Process"
--- modules.
+-- POSIX process support.  See also the System.Cmd and System.Process
+-- modules in the process package.
 --
 -----------------------------------------------------------------------------
 
diff --git a/System/Posix/Signals.hs b/System/Posix/Signals.hs
--- a/System/Posix/Signals.hs
+++ b/System/Posix/Signals.hs
@@ -97,10 +97,11 @@
 import System.IO.Unsafe
 import System.Posix.Types
 import System.Posix.Internals
+import Control.Concurrent (withMVar)
 
 #ifdef __GLASGOW_HASKELL__
 #include "Signals.h"
-import GHC.Conc	( ensureIOManagerIsRunning )
+import GHC.Conc	( ensureIOManagerIsRunning, signalHandlerLock )
 #endif
 
 -- -----------------------------------------------------------------------------
@@ -322,6 +323,8 @@
         Just (SignalSet x) -> withForeignPtr x $ install' 
   where 
     install' mask = 
+         -- prevent race with the IO manager thread, see #1922
+      withMVar signalHandlerLock $ \_ ->
       alloca $ \p_sp -> do
 
       rc <- case handler of
diff --git a/System/Posix/User.hsc b/System/Posix/User.hsc
--- a/System/Posix/User.hsc
+++ b/System/Posix/User.hsc
@@ -55,6 +55,10 @@
 #ifdef HAVE_GETPWENT
 import Control.Exception
 #endif
+#ifdef HAVE_GETGRNAM_R
+import Control.Monad
+import System.IO.Error
+#endif
 
 -- -----------------------------------------------------------------------------
 -- user environemnt
@@ -187,13 +191,18 @@
 getGroupEntryForName name = do
   allocaBytes (#const sizeof(struct group)) $ \pgr ->
     allocaBytes grBufSize $ \pbuf ->
-      alloca $ \ ppgr -> 
-	withCString name $ \ pstr -> do
+      alloca $ \ ppgr ->
+        withCString name $ \ pstr -> do
           throwErrorIfNonZero_ "getGroupEntryForName" $
-	     c_getgrnam_r pstr pgr pbuf (fromIntegral grBufSize) ppgr
-	  throwErrnoIfNull "getGroupEntryForName" $
-	     peekElemOff ppgr 0
-	  unpackGroupEntry pgr
+            c_getgrnam_r pstr pgr pbuf (fromIntegral grBufSize) ppgr
+          r <- peekElemOff ppgr 0
+          when (r == nullPtr) $
+            ioError $ flip ioeSetErrorString "no group name"
+                    $ mkIOError doesNotExistErrorType
+                                "getGroupEntryForName"
+                                Nothing
+                                (Just name)
+          unpackGroupEntry pgr
 
 foreign import ccall unsafe "getgrnam_r"
   c_getgrnam_r :: CString -> Ptr CGroup -> CString
diff --git a/unix.cabal b/unix.cabal
--- a/unix.cabal
+++ b/unix.cabal
@@ -1,5 +1,5 @@
 name:		unix
-version:	2.2.0.0
+version:	2.3.0.0
 license:	BSD3
 license-file:	LICENSE
 maintainer:	libraries@haskell.org