diff --git a/main/Act2.hs b/main/Act2.hs
--- a/main/Act2.hs
+++ b/main/Act2.hs
@@ -8,6 +8,7 @@
 import           Codec.Compression.GZip
 import           Control.Concurrent
 import           Control.Concurrent.Async
+import           Control.Concurrent.STM
 import           Control.Monad.Trans.Resource
 import           Data.Aeson.Encode
 import           Data.ByteString ( length )
@@ -110,11 +111,11 @@
           cd dir
           maybe (return ()) (uncurry $ run_ . fromText) $ uncons $ words cmdline
 
-watchdog :: MVar UTCTime -> Int -> IO ()
+watchdog :: TVar UTCTime -> Int -> IO ()
 watchdog timestamp duration =
   forever $ do
     now <- getCurrentTime
-    now' <- readMVar timestamp
+    now' <- atomically $ readTVar timestamp
     when (diffUTCTime now now' > fromIntegral duration) $
       throwIO $ userError "watchdog expired"
     threadDelay 1000000
@@ -123,10 +124,11 @@
 call Args{..} = do
   config <- decodeFile aConfig >>= maybeThrow (userError "Bad Config")
   env <- flowEnv config
-  timestamp <- newEmptyMVar
-  void $ concurrently (watchdog timestamp aTimeout) $ do
+  now <- getCurrentTime
+  timestamp <- atomically $ newTVar now
+  void $ concurrently (watchdog timestamp aTimeout) $
     forever $ runResourceT $ runFlowT env $ do
-      liftIO $ getCurrentTime >>= putMVar timestamp
+      liftIO $ getCurrentTime >>= atomically . writeTVar timestamp
       act aQueue $ exec aCommandLine
 
 main :: IO ()
diff --git a/wolf.cabal b/wolf.cabal
--- a/wolf.cabal
+++ b/wolf.cabal
@@ -1,5 +1,5 @@
 name:                wolf
-version:             0.2.9
+version:             0.2.10
 synopsis:            Amazon Simple Workflow Service Wrapper.
 homepage:            https://github.com/swift-nav/wolf
 license:             MIT
@@ -177,6 +177,7 @@
                      , optparse-applicative
                      , resourcet
                      , shelly
+                     , stm
                      , system-filepath
                      , text
                      , time