diff --git a/Test/QuickCheck/Parallel.hs b/Test/QuickCheck/Parallel.hs
--- a/Test/QuickCheck/Parallel.hs
+++ b/Test/QuickCheck/Parallel.hs
@@ -1,4 +1,7 @@
 {-# LANGUAGE CPP #-}
+#if __GLASGOW_HASKELL__ >= 701
+{-# LANGUAGE Trustworthy #-}
+#endif
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Test.QuickCheck.Parallel
@@ -32,9 +35,8 @@
 import Test.QuickCheck.State
 
 import Control.Concurrent
-#if   __GLASGOW_HASKELL__ < 702
+#if   __GLASGOW_HASKELL__ < 704
 import GHC.Conc           (numCapabilities, forkOnIO)
-#elif __GLASGOW_HASKELL__ < 704
 #else
 import GHC.Conc           (getNumProcessors, setNumCapabilities)
 #endif
@@ -74,7 +76,7 @@
 --
 pRun'  :: Int -> [Test] -> IO ()
 pRun' depth tests = do
-#if __GLASGOW_HASKELL__ >= 702
+#if __GLASGOW_HASKELL__ >= 704
     num <- getNumCapabilities
 #else
     let num = numCapabilities
@@ -84,13 +86,9 @@
 -- | Variant of 'pRunWithNum'. Run a list of QuickCheck properties in parallel
 -- chunks, using all Processors.
 pRunAllProcessors  :: Int -> [Test] -> IO ()
-#if   __GLASGOW_HASKELL__ < 702
+#if   __GLASGOW_HASKELL__ < 704
 pRunAllProcessors depth tests
   = pRunInternal forkOnIO numCapabilities depth tests
-#elif __GLASGOW_HASKELL__ < 704
-pRunAllProcessors depth tests = do
-    caps <- getNumCapabilities
-    pRunInternal forkOn caps depth tests
 #else
 pRunAllProcessors depth tests = do
     caps <- getNumCapabilities
diff --git a/pqc.cabal b/pqc.cabal
--- a/pqc.cabal
+++ b/pqc.cabal
@@ -1,5 +1,5 @@
 name:                pqc
-version:             0.5
+version:             0.5.1
 description:         Parallel batch driver for QuickCheck
 synopsis:            Parallel batch driver for QuickCheck
 category:            Testing