diff --git a/src/Data/Opentracing/Tracer.hs b/src/Data/Opentracing/Tracer.hs
--- a/src/Data/Opentracing/Tracer.hs
+++ b/src/Data/Opentracing/Tracer.hs
@@ -18,7 +18,7 @@
 import qualified Data.HashMap.Lazy      as HM
 import           Data.Opentracing.Types
 import           Data.Text              (Text, justifyRight, pack)
-import           Data.Time
+import           Data.Time.Clock.POSIX
 import           Data.Word
 import           Numeric
 import           System.Random
@@ -42,10 +42,14 @@
   context     <- askSpanContext
   newSpan' name context []
 
+
+getNow :: MonadIO m => m Int
+getNow = liftIO $ (round . (* 1000)) <$> getPOSIXTime
+
 newSpan' :: MonadTracer m => SpanName -> SpanContext -> [SpanReference] -> m Span
 newSpan' name context references = do
   spanId      <- if null references then return (traceId context) else newId
-  startTime   <- liftIO getCurrentTime
+  startTime   <- getNow
   let finishTime = Nothing
       tags       = HM.empty
       logs       = HM.empty
@@ -73,7 +77,7 @@
 
 finishSpan :: MonadTracer m => Span -> m Span
 finishSpan Span{..} = do
-  ts <- liftIO getCurrentTime
+  ts <- getNow
   return Span {finishTime = Just ts, ..}
 
 newContext :: MonadIO m => m SpanContext
diff --git a/src/Data/Opentracing/Types.hs b/src/Data/Opentracing/Types.hs
--- a/src/Data/Opentracing/Types.hs
+++ b/src/Data/Opentracing/Types.hs
@@ -3,7 +3,6 @@
 import qualified Data.HashMap.Lazy as HM
 import           Data.Scientific
 import           Data.Text         (Text)
-import           Data.Time
 
 data SpanTag
   = TagString Text
@@ -29,8 +28,8 @@
 data Span = Span
   { spanId     :: Text
   , name       :: Text
-  , startTime  :: UTCTime
-  , finishTime :: Maybe UTCTime
+  , startTime  :: Int
+  , finishTime :: Maybe Int
   , tags       :: HM.HashMap Text SpanTag
   , logs       :: HM.HashMap Text Text
   , context    :: SpanContext
diff --git a/src/Yam/Middleware/Trace.hs b/src/Yam/Middleware/Trace.hs
--- a/src/Yam/Middleware/Trace.hs
+++ b/src/Yam/Middleware/Trace.hs
@@ -78,14 +78,17 @@
 hSampled :: HeaderName
 hSampled = "X-B3-Sampled"
 
-parseSpan :: RequestHeaders -> Env -> Env
+parseSpan :: RequestHeaders -> Env -> IO Env
 parseSpan headers env =
   let sc = fromMaybe (SpanContext "" HM.empty) $ getAttr spanContextKey env
   in case lookup hTraceId headers of
       Just tid -> let sc' = sc { traceId = decodeUtf8 tid }
-                  in env & setAttr spanContextKey      sc'
-                         & go (maybe (traceId sc') decodeUtf8 $ lookup hSpanId headers) sc'
-      _        -> env
+                  in return $ env
+                      & setAttr spanContextKey      sc'
+                      & go (maybe (traceId sc') decodeUtf8 $ lookup hSpanId headers) sc'
+      _        -> do
+        c <- newContext
+        return $ setAttr spanContextKey c env
   where
     go spanId context env' =
       let name = "-"
@@ -97,21 +100,20 @@
       in setAttr spanKey Span{..} env'
 
 traceMw :: Env -> (Span -> App ()) -> Middleware
-traceMw env notify app req resH = runApp (parseSpan (requestHeaders req) env) $
-  runInSpan ((decodeUtf8 $ requestMethod req) <> " /" <> T.intercalate "/" (pathInfo req)) notify $ \s@Span{..} -> do
-    let SpanContext{..} = context
-        tid = traceId <> "," <> spanId
-        v   = L.insert extensionLogKey tid (vault req)
-        v'  = L.insert spanKey s v
-    liftIO $ app req {vault = v'}
-      $ resH . mapResponseHeaders (\hs -> (hTraceId,encodeUtf8 traceId):(hSpanId, encodeUtf8 spanId):hs)
+traceMw env' notify app req resH = do
+  env <- parseSpan (requestHeaders req) env'
+  runApp env $
+    runInSpan ((decodeUtf8 $ requestMethod req) <> " /" <> T.intercalate "/" (pathInfo req)) notify $ \s@Span{..} -> do
+      let SpanContext{..} = context
+          tid = traceId <> "," <> spanId
+          v   = L.insert extensionLogKey tid (vault req)
+          v'  = L.insert spanKey s v
+      liftIO $ app req {vault = v'}
+        $ resH . mapResponseHeaders (\hs -> (hTraceId,encodeUtf8 traceId):(hSpanId, encodeUtf8 spanId):hs)
 
 traceMiddleware :: TraceConfig -> AppMiddleware
 traceMiddleware TraceConfig{..}
   = AppMiddleware $ \env f -> if enabled
-    then do
-      c <- newContext
-      let env' = setAttr spanContextKey c env
-      f (env', traceMw env' $ notifier method)
+    then f (env, traceMw env $ notifier method)
     else f (env, id)
 
diff --git a/yam.cabal b/yam.cabal
--- a/yam.cabal
+++ b/yam.cabal
@@ -1,6 +1,6 @@
 cabal-version: 1.12
 name: yam
-version: 0.5.4
+version: 0.5.5
 license: BSD3
 license-file: LICENSE
 copyright: (c) 2018 Daniel YU
@@ -50,7 +50,7 @@
                  -fno-warn-missing-signatures
     build-depends:
         aeson >=1.4.2.0 && <1.5,
-        base >=4.7 && <5,
+        base >=4.11 && <5,
         bytestring >=0.10.8.2 && <0.11,
         data-default >=0.7.1.1 && <0.8,
         fast-logger >=2.4.13 && <2.5,
@@ -60,7 +60,7 @@
         mtl >=2.2.2 && <2.3,
         random ==1.1.*,
         reflection >=2.1.4 && <2.2,
-        salak >=0.1.4 && <0.2,
+        salak >=0.1.4 && <0.3,
         scientific >=0.3.6.2 && <0.4,
         servant-server ==0.15.*,
         servant-swagger >=1.1.7 && <1.2,
@@ -113,7 +113,7 @@
     build-depends:
         QuickCheck >=2.12.6.1 && <2.13,
         aeson >=1.4.2.0 && <1.5,
-        base >=4.7 && <5,
+        base >=4.11 && <5,
         bytestring >=0.10.8.2 && <0.11,
         data-default >=0.7.1.1 && <0.8,
         fast-logger >=2.4.13 && <2.5,
@@ -124,7 +124,7 @@
         mtl >=2.2.2 && <2.3,
         random ==1.1.*,
         reflection >=2.1.4 && <2.2,
-        salak >=0.1.4 && <0.2,
+        salak >=0.1.4 && <0.3,
         scientific >=0.3.6.2 && <0.4,
         servant-server ==0.15.*,
         servant-swagger >=1.1.7 && <1.2,