diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,9 @@
 
+Version 0.7
+-----
+
+* More precise handling of transact priorities.
+
 Version 0.6.1
 -----
 
diff --git a/Simulation/Aivika/GPSS/Block/Generate.hs b/Simulation/Aivika/GPSS/Block/Generate.hs
--- a/Simulation/Aivika/GPSS/Block/Generate.hs
+++ b/Simulation/Aivika/GPSS/Block/Generate.hs
@@ -45,7 +45,8 @@
                         -> Int
                         -- ^ the transact priority
                         -> GeneratorBlock (Transact a)
-streamGeneratorBlock s = streamGeneratorBlockM s . return
+streamGeneratorBlock s priority = streamGeneratorBlockM s' (return priority)
+  where s' = Cons $ processWithPriority priority >> runStream s
 
 -- | Return a generator block by the specified stream using zero priority.
 streamGeneratorBlock0 :: Stream (Arrival a)
diff --git a/Simulation/Aivika/GPSS/Block/Priority.hs b/Simulation/Aivika/GPSS/Block/Priority.hs
--- a/Simulation/Aivika/GPSS/Block/Priority.hs
+++ b/Simulation/Aivika/GPSS/Block/Priority.hs
@@ -23,4 +23,4 @@
                  -- ^ the priority
                  -> Block (Transact a) (Transact a)
 priorityBlock priority =
-  Block { blockProcess = \a -> return (assignTransactPriority a priority) }
+  Block { blockProcess = \a -> assignTransactPriority a priority }
diff --git a/Simulation/Aivika/GPSS/Transact.hs b/Simulation/Aivika/GPSS/Transact.hs
--- a/Simulation/Aivika/GPSS/Transact.hs
+++ b/Simulation/Aivika/GPSS/Transact.hs
@@ -36,6 +36,8 @@
 import Control.Exception
 
 import Data.IORef
+import Data.Functor
+
 import qualified Data.HashMap.Lazy as HM
 
 import Simulation.Aivika
@@ -73,6 +75,9 @@
 instance Eq (Transact a) where
   x == y = (transactProcessIdRef x) == (transactProcessIdRef y)
 
+instance Functor Transact where
+  fmap f t = t { transactValue = f (transactValue t) }
+
 -- | Create a new transact.
 newTransact :: Arrival a
                -- ^ the arrival data
@@ -133,7 +138,7 @@
 takeTransact :: Transact a -> Process ()
 takeTransact t =
   Process $ \pid ->
-  Cont $ \c ->
+  Cont $ \c0 ->
   Event $ \p ->
   do pid0 <- readIORef (transactProcessIdRef t)
      case pid0 of
@@ -142,11 +147,17 @@
          SimulationRetry
          "The transact is acquired by another process: takeTransact"
        Nothing   ->
-         do writeIORef (transactProcessIdRef t) (Just pid)
+         do let priority = transactPriority t
+            writeIORef (transactProcessIdRef t) (Just pid)
             n <- readIORef (transactPreemptionCountRef t)
             if n == 0
-              then invokeEvent p $ resumeCont c ()
-              else do c <- invokeEvent p $
+              then if priority == pointPriority p
+                   then invokeEvent p $
+                        resumeCont c0 ()
+                   else invokeEvent p $
+                        resumeCont (substituteContPriority c0 priority) ()
+              else do let c = substituteContPriority c0 priority
+                      c <- invokeEvent p $
                            freezeContReentering c () $
                            invokeCont c $
                            invokeProcess pid $
@@ -286,9 +297,10 @@
      return t { transactValue = b }
 
 -- | Assign the priority and return a new version of the same transact.
-assignTransactPriority :: Transact a -> Int -> Transact a
+assignTransactPriority :: Transact a -> Int -> Process (Transact a)
 assignTransactPriority t priority =
-  t { transactPriority = priority }
+  do processWithPriority priority
+     return t { transactPriority = priority }
 
 -- | Reactivate the transacts or transfer them to the specified computations.
 reactivateTransacts :: [(Transact a, Maybe (Process ()))] -> Event ()
diff --git a/Simulation/Aivika/Trans/GPSS/AssemblySet.hs b/Simulation/Aivika/Trans/GPSS/AssemblySet.hs
--- a/Simulation/Aivika/Trans/GPSS/AssemblySet.hs
+++ b/Simulation/Aivika/Trans/GPSS/AssemblySet.hs
@@ -50,7 +50,7 @@
   {-# INLINABLE (==) #-}
   x == y = (assemblySetAssemblingTransact x) == (assemblySetAssemblingTransact y)
 
-instance Hashable (AssemblySet m) where
+instance MonadDES m => Hashable (AssemblySet m) where
   hashWithSalt salt x = hashWithSalt salt (assemblySetSequenceNo x)
 
 -- | Create a new assembly set.
diff --git a/Simulation/Aivika/Trans/GPSS/Block/Generate.hs b/Simulation/Aivika/Trans/GPSS/Block/Generate.hs
--- a/Simulation/Aivika/Trans/GPSS/Block/Generate.hs
+++ b/Simulation/Aivika/Trans/GPSS/Block/Generate.hs
@@ -49,7 +49,8 @@
                         -- ^ the transact priority
                         -> GeneratorBlock m (Transact m a)
 {-# INLINABLE streamGeneratorBlock #-}
-streamGeneratorBlock s = streamGeneratorBlockM s . return
+streamGeneratorBlock s priority = streamGeneratorBlockM s' (return priority)
+  where s' = Cons $ processWithPriority priority >> runStream s
 
 -- | Return a generator block by the specified stream using zero priority.
 streamGeneratorBlock0 :: MonadDES m
diff --git a/Simulation/Aivika/Trans/GPSS/Block/Priority.hs b/Simulation/Aivika/Trans/GPSS/Block/Priority.hs
--- a/Simulation/Aivika/Trans/GPSS/Block/Priority.hs
+++ b/Simulation/Aivika/Trans/GPSS/Block/Priority.hs
@@ -25,4 +25,4 @@
                  -> Block m (Transact m a) (Transact m a)
 {-# INLINABLE priorityBlock #-}
 priorityBlock priority =
-  Block { blockProcess = \a -> return (assignTransactPriority a priority) }
+  Block { blockProcess = \a -> assignTransactPriority a priority }
diff --git a/Simulation/Aivika/Trans/GPSS/Queue.hs b/Simulation/Aivika/Trans/GPSS/Queue.hs
--- a/Simulation/Aivika/Trans/GPSS/Queue.hs
+++ b/Simulation/Aivika/Trans/GPSS/Queue.hs
@@ -94,7 +94,7 @@
 instance MonadDES m => Eq (Queue m) where
   x == y = (queueContentRef x) == (queueContentRef y)
 
-instance Hashable (Queue m) where
+instance MonadDES m => Hashable (Queue m) where
   hashWithSalt salt x = hashWithSalt salt (queueSequenceNo x)
 
 -- | Create a new queue.
diff --git a/Simulation/Aivika/Trans/GPSS/Queue.hs-boot b/Simulation/Aivika/Trans/GPSS/Queue.hs-boot
--- a/Simulation/Aivika/Trans/GPSS/Queue.hs-boot
+++ b/Simulation/Aivika/Trans/GPSS/Queue.hs-boot
@@ -38,6 +38,6 @@
              }
 
 instance MonadDES m => Eq (Queue m)
-instance Hashable (Queue m)
+instance MonadDES m => Hashable (Queue m)
 
 instance MonadDES m => Eq (QueueEntry m)
diff --git a/Simulation/Aivika/Trans/GPSS/Transact.hs b/Simulation/Aivika/Trans/GPSS/Transact.hs
--- a/Simulation/Aivika/Trans/GPSS/Transact.hs
+++ b/Simulation/Aivika/Trans/GPSS/Transact.hs
@@ -35,6 +35,8 @@
 import Control.Monad.Trans
 import Control.Exception
 
+import Data.Functor
+
 import qualified Data.HashMap.Lazy as HM
 
 import Simulation.Aivika.Trans
@@ -74,6 +76,11 @@
   {-# INLINABLE (==) #-}
   x == y = (transactProcessIdRef x) == (transactProcessIdRef y)
 
+instance MonadDES m => Functor (Transact m) where
+
+  {-# INLINABLE fmap #-}
+  fmap f t = t { transactValue = f (transactValue t) }
+
 -- | Create a new transact.
 newTransact :: MonadDES m
                => Arrival a
@@ -139,7 +146,7 @@
 {-# INLINABLE takeTransact #-}
 takeTransact t =
   Process $ \pid ->
-  Cont $ \c ->
+  Cont $ \c0 ->
   Event $ \p ->
   do pid0 <- invokeEvent p $ readRef (transactProcessIdRef t)
      case pid0 of
@@ -148,11 +155,17 @@
          SimulationRetry
          "The transact is acquired by another process: takeTransact"
        Nothing   ->
-         do invokeEvent p $ writeRef (transactProcessIdRef t) (Just pid)
+         do let priority = transactPriority t
+            invokeEvent p $ writeRef (transactProcessIdRef t) (Just pid)
             n <- invokeEvent p $ readRef (transactPreemptionCountRef t)
             if n == 0
-              then invokeEvent p $ resumeCont c ()
-              else do c <- invokeEvent p $
+              then if priority == pointPriority p
+                   then invokeEvent p $
+                        resumeCont c0 ()
+                   else invokeEvent p $
+                        resumeCont (substituteContPriority c0 priority) ()
+              else do let c = substituteContPriority c0 priority
+                      c <- invokeEvent p $
                            freezeContReentering c () $
                            invokeCont c $
                            invokeProcess pid $
@@ -300,9 +313,11 @@
      return t { transactValue = b }
 
 -- | Assign the priority and return a new version of the same transact.
-assignTransactPriority :: Transact m a -> Int -> Transact m a
+assignTransactPriority :: MonadDES m => Transact m a -> Int -> Process m (Transact m a)
+{-# INLINABLE assignTransactPriority #-}
 assignTransactPriority t priority =
-  t { transactPriority = priority }
+  do processWithPriority priority
+     return t { transactPriority = priority }
 
 -- | Reactivate the transacts or transfer them to the specified computations.
 reactivateTransacts :: MonadDES m => [(Transact m a, Maybe (Process m ()))] -> Event m ()
diff --git a/aivika-gpss.cabal b/aivika-gpss.cabal
--- a/aivika-gpss.cabal
+++ b/aivika-gpss.cabal
@@ -1,5 +1,5 @@
 name:            aivika-gpss
-version:         0.6.2
+version:         0.7.1
 synopsis:        GPSS-like DSL for Aivika
 description:
     This package allows defining simulation models in terms of a GPSS-like
@@ -40,10 +40,10 @@
 category:        Simulation
 license:         BSD3
 license-file:    LICENSE
-copyright:       (c) 2017-2018. David Sorokin <david.sorokin@gmail.com>
+copyright:       (c) 2017-2023. David Sorokin <davsor@mail.ru>
 author:          David Sorokin
-maintainer:      David Sorokin <david.sorokin@gmail.com>
-homepage:        http://www.aivikasoft.com
+maintainer:      David Sorokin <davsor@mail.ru>
+homepage:        https://gitflic.ru/project/dsorokin/aivika-gpss
 cabal-version:   >= 1.10
 build-type:      Simple
 tested-with:     GHC == 8.0.1
@@ -145,8 +145,8 @@
                      containers >= 0.4.0.0,
                      hashable >= 1.2.0.0,
                      unordered-containers >= 0.1.0.0,
-                     aivika >= 5.9.1,
-                     aivika-transformers >= 5.9.1
+                     aivika >= 6.0.0,
+                     aivika-transformers >= 6.0.0
 
     other-extensions:   MultiParamTypeClasses,
                         TypeFamilies,
@@ -161,5 +161,5 @@
 source-repository head
 
     type:     git
-    location: https://github.com/dsorokin/aivika-gpss
+    location: https://gitflic.ru/project/dsorokin/aivika-gpss