diff --git a/chronos/asyncloop.nim b/chronos/asyncloop.nim
index 6fee704..7f10a9a 100644
--- a/chronos/asyncloop.nim
+++ b/chronos/asyncloop.nim
@@ -11,7 +11,7 @@
 include "system/inclrtl"
 
 import os, tables, strutils, heapqueue, lists, options, nativesockets, net,
-       deques
+       deques, sequtils
 import timer
 
 export Port, SocketFlag
@@ -190,9 +190,12 @@ type
   AsyncTimeoutError* = object of AsyncError
     ## Timeout exception
 
-  TimerCallback* = object
+  TimerHandle* = distinct Natural
+
+  TimerCallback* = ref object
     finishAt*: Moment
     function*: AsyncCallback
+    removed: bool
 
   TrackerBase* = ref object of RootRef
     id*: string
@@ -203,6 +206,7 @@ type
     timers*: HeapQueue[TimerCallback]
     callbacks*: Deque[AsyncCallback]
     trackers*: Table[string, TrackerBase]
+    timerHandles: seq[TimerCallback]
 
 proc `<`(a, b: TimerCallback): bool =
   result = a.finishAt < b.finishAt
@@ -227,14 +231,27 @@ func getAsyncTimestamp*(a: Duration): auto {.inline.} =
     result = cast[int32](res)
     result += min(1, cast[int32](mid))
 
+template removeTimers(loop) =
+  var timers = cast[seq[TimerCallback]](loop.timers)
+  timers.keepItIf( not(it.removed) )
+  loop.timers = cast[HeapQueue[TimerCallback]](timers)
+
 template processTimersGetTimeout(loop, timeout: untyped) =
   var count = len(loop.timers)
   if count > 0:
     var lastFinish = curTime
     while count > 0:
+      if loop.timers.len < 1:
+        break
+
+      if loop.timers[0].removed:
+        discard loop.timers.pop()
+        continue
+
       lastFinish = loop.timers[0].finishAt
       if curTime < lastFinish:
         break
+
       loop.callbacks.addLast(loop.timers.pop().function)
       dec(count)
     if count > 0:
@@ -255,6 +272,13 @@ template processTimers(loop: untyped) =
   var count = len(loop.timers)
   if count > 0:
     while count > 0:
+      if loop.timers.len < 1:
+        break
+
+      if loop.timers[0].removed:
+        discard loop.timers.pop()
+        continue
+
       if curTime < loop.timers[0].finishAt:
         break
       loop.callbacks.addLast(loop.timers.pop().function)
@@ -721,11 +745,44 @@ elif unixPlatform:
     # poll() call.
     loop.processCallbacks()
 
+    # Cleanup canceled timers
+    loop.removeTimers()
+
 else:
   proc initAPI() = discard
   proc globalInit() = discard
 
-proc addTimer*(at: Moment, cb: CallbackFunc, udata: pointer = nil) =
+proc setTimer*(at: Moment, cb: CallbackFunc, udata: pointer = nil): TimerHandle =
+  ## Arrange for the callback ``cb`` to be called at the given absolute
+  ## timestamp ``at``. You can also pass ``udata`` to callback.
+  let loop = getGlobalDispatcher()
+
+  var timer = TimerCallback(finishAt: at,
+                            function: AsyncCallback(function: cb, udata: udata))
+  loop.timerHandles.add(timer)
+  result = TimerHandle(loop.timerHandles.len - 1)
+
+  # try to optimize for the case where the top
+  # element is already removed and just replace it
+  if loop.timers.len > 0 and loop.timers[0].removed:
+    discard loop.timers.replace(timer)
+  else:
+    loop.timers.push(timer)
+
+proc clearTimer*(handle: TimerHandle) =
+  var loop = getGlobalDispatcher()
+  var timer = loop.timerHandles[handle.Natural]
+  loop.timerHandles[handle.Natural] = nil
+
+  # optimize for handle being at the top
+  if timer == loop.timers[0]:
+    discard loop.timers.pop()
+  else:
+    timer.removed = true
+
+proc addTimer*(at: Moment, cb: CallbackFunc, udata: pointer = nil) {.
+    deprecated: "Use setTimer/clearTimer pairs"
+  .} =
   ## Arrange for the callback ``cb`` to be called at the given absolute
   ## timestamp ``at``. You can also pass ``udata`` to callback.
   let loop = getGlobalDispatcher()
@@ -770,6 +827,7 @@ proc sleepAsync*(duration: Duration): Future[void] =
   ## ``duration`` time.
   var retFuture = newFuture[void]("chronos.sleepAsync(Duration)")
   let moment = Moment.fromNow(duration)
+  var timer: TimerHandle
 
   proc completion(data: pointer) {.gcsafe.} =
     if not(retFuture.finished()):
@@ -777,10 +835,10 @@ proc sleepAsync*(duration: Duration): Future[void] =
 
   proc cancel(udata: pointer) {.gcsafe.} =
     if not(retFuture.finished()):
-      removeTimer(moment, completion, cast[pointer](retFuture))
+      clearTimer(timer)
 
   retFuture.cancelCallback = cancel
-  addTimer(moment, completion, cast[pointer](retFuture))
+  timer = setTimer(moment, completion, cast[pointer](retFuture))
   return retFuture
 
 proc sleepAsync*(ms: int): Future[void] {.
@@ -797,6 +855,7 @@ proc withTimeout*[T](fut: Future[T], timeout: Duration): Future[bool] =
   var retFuture = newFuture[bool]("chronos.`withTimeout`")
   var moment: Moment
   var timerPresent = false
+  var timer: TimerHandle
 
   proc continuation(udata: pointer) {.gcsafe.} =
     if not(retFuture.finished()):
@@ -808,13 +867,13 @@ proc withTimeout*[T](fut: Future[T], timeout: Duration): Future[bool] =
       else:
         # Future `fut` completed/failed/cancelled first.
         if timerPresent:
-          removeTimer(moment, continuation, nil)
+          clearTimer(timer)
         retFuture.complete(true)
 
   proc cancel(udata: pointer) {.gcsafe.} =
     if not(retFuture.finished()):
       if timerPresent:
-        removeTimer(moment, continuation, nil)
+        clearTimer(timer)
       if not(fut.finished()):
         fut.removeCallback(continuation)
         fut.cancel()
@@ -831,7 +890,7 @@ proc withTimeout*[T](fut: Future[T], timeout: Duration): Future[bool] =
       timerPresent = true
       moment = Moment.fromNow(timeout)
       retFuture.cancelCallback = cancel
-      addTimer(moment, continuation, nil)
+      timer = setTimer(moment, continuation, nil)
       fut.addCallback(continuation)
 
   return retFuture
@@ -851,7 +910,8 @@ proc wait*[T](fut: Future[T], timeout = InfiniteDuration): Future[T] =
   ## should return, because it can't be cancelled too.
   var retFuture = newFuture[T]("chronos.wait()")
   var moment: Moment
-  var timerPresent = false
+  var timerPresent: bool
+  var timer: TimerHandle
 
   proc continuation(udata: pointer) {.gcsafe.} =
     if not(retFuture.finished()):
@@ -859,11 +919,13 @@ proc wait*[T](fut: Future[T], timeout = InfiniteDuration): Future[T] =
         # Timer exceeded first.
         fut.removeCallback(continuation)
         fut.cancel()
+        if timerPresent:
+          clearTimer(timer)
         retFuture.fail(newException(AsyncTimeoutError, "Timeout exceeded!"))
       else:
         # Future `fut` completed/failed/cancelled first.
         if timerPresent:
-          removeTimer(moment, continuation, nil)
+          clearTimer(timer)
 
         if fut.failed():
           retFuture.fail(fut.error)
@@ -876,7 +938,7 @@ proc wait*[T](fut: Future[T], timeout = InfiniteDuration): Future[T] =
   proc cancel(udata: pointer) {.gcsafe.} =
     if not(retFuture.finished()):
       if timerPresent:
-        removeTimer(moment, continuation, nil)
+        clearTimer(timer)
       if not(fut.finished()):
         fut.removeCallback(continuation)
         fut.cancel()
@@ -896,10 +958,10 @@ proc wait*[T](fut: Future[T], timeout = InfiniteDuration): Future[T] =
       retFuture.cancelCallback = cancel
       fut.addCallback(continuation)
     else:
-      timerPresent = true
       moment = Moment.fromNow(timeout)
       retFuture.cancelCallback = cancel
-      addTimer(moment, continuation, nil)
+      timer = setTimer(moment, continuation, nil)
+      timerPresent = true
       fut.addCallback(continuation)
 
   return retFuture