diff --git a/chronos/asyncloop.nim b/chronos/asyncloop.nim
index 515a446a..5ba56a77 100644
--- a/chronos/asyncloop.nim
+++ b/chronos/asyncloop.nim
@@ -362,13 +362,13 @@ when defined(windows) or defined(nimdoc):
     ## Creates a new Dispatcher instance.
     new result
     result.ioPort = createIoCompletionPort(INVALID_HANDLE_VALUE, 0, 0, 1)
-    when compiles(initHashSet):
+    when declared(initHashSet):
       # After 0.20.0 Nim's stdlib version
       result.handles = initHashSet[AsyncFD]()
     else:
       # Pre 0.20.0 Nim's stdlib version
       result.handles = initSet[AsyncFD]()
-    when compiles(initHeapQueue):
+    when declared(initHeapQueue):
       # After 0.20.0 Nim's stdlib version
       result.timers = initHeapQueue[TimerCallback]()
     else:
@@ -510,7 +510,12 @@ elif unixPlatform:
     ## Create new dispatcher.
     new result
     result.selector = newSelector[SelectorData]()
-    result.timers.newHeapQueue()
+    when declared(initHeapQueue):
+      # After 0.20.0 Nim's stdlib version
+      result.timers = initHeapQueue()
+    else:
+      # Before 0.20.0 Nim's stdlib version
+      result.timers.newHeapQueue()
     result.callbacks = initDeque[AsyncCallback](64)
     result.keys = newSeq[ReadyKey](64)
     result.trackers = initTable[string, TrackerBase]()
diff --git a/tests/testaddress.nim b/tests/testaddress.nim
index 7855a21d..56c9f827 100644
--- a/tests/testaddress.nim
+++ b/tests/testaddress.nim
@@ -8,6 +8,8 @@
 import strutils, unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "TransportAddress test suite":
   test "initTAddress(string)":
     check $initTAddress("0.0.0.0:1") == "0.0.0.0:1"
diff --git a/tests/testasyncstream.nim b/tests/testasyncstream.nim
index 7b52df5d..a5c7a04e 100644
--- a/tests/testasyncstream.nim
+++ b/tests/testasyncstream.nim
@@ -8,6 +8,8 @@
 import strutils, unittest, os
 import ../chronos, ../chronos/streams/tlsstream
 
+when defined(nimHasUsed): {.used.}
+
 const SelfSignedRsaKey = """
 -----BEGIN PRIVATE KEY-----
 MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQDSXcKMR6zIIHSy
diff --git a/tests/testbugs.nim b/tests/testbugs.nim
index 3a78f8b9..6154d3b5 100644
--- a/tests/testbugs.nim
+++ b/tests/testbugs.nim
@@ -8,6 +8,8 @@
 import unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "Asynchronous issues test suite":
   const HELLO_PORT = 45679
   const TEST_MSG = "testmsg"
diff --git a/tests/testdatagram.nim b/tests/testdatagram.nim
index b2dfec09..3cde640b 100644
--- a/tests/testdatagram.nim
+++ b/tests/testdatagram.nim
@@ -8,6 +8,8 @@
 import strutils, net, unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "Datagram Transport test suite":
   const
     TestsCount = 2000
diff --git a/tests/testfut.nim b/tests/testfut.nim
index ad0fa3e1..d0725b24 100644
--- a/tests/testfut.nim
+++ b/tests/testfut.nim
@@ -8,6 +8,8 @@
 import unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "Future[T] behavior test suite":
   proc testFuture1(): Future[int] {.async.} =
     await sleepAsync(0.milliseconds)
diff --git a/tests/testmacro.nim b/tests/testmacro.nim
index ac509832..19e8e498 100644
--- a/tests/testmacro.nim
+++ b/tests/testmacro.nim
@@ -8,6 +8,8 @@
 import unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 proc asyncRetValue(n: int): Future[int] {.async.} =
   await sleepAsync(n.milliseconds)
   result = n * 10
diff --git a/tests/testnet.nim b/tests/testnet.nim
index 5d001611..76139ac5 100644
--- a/tests/testnet.nim
+++ b/tests/testnet.nim
@@ -8,6 +8,8 @@
 import unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "Network utilities test suite":
 
   const MaskVectors = [
diff --git a/tests/testserver.nim b/tests/testserver.nim
index d1cadd28..890208d1 100644
--- a/tests/testserver.nim
+++ b/tests/testserver.nim
@@ -8,6 +8,8 @@
 import strutils, unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "Server's test suite":
   type
     CustomServer = ref object of StreamServer
diff --git a/tests/testsignal.nim b/tests/testsignal.nim
index 0b7d64d2..b8605568 100644
--- a/tests/testsignal.nim
+++ b/tests/testsignal.nim
@@ -8,6 +8,8 @@
 import unittest, strutils
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 when not defined(windows):
   import posix
 
diff --git a/tests/testsoon.nim b/tests/testsoon.nim
index b8a79e7e..dfa712b3 100644
--- a/tests/testsoon.nim
+++ b/tests/testsoon.nim
@@ -8,6 +8,8 @@
 import unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "callSoon() tests suite":
   const CallSoonTests = 10
   var soonTest1 = 0'u
diff --git a/tests/teststream.nim b/tests/teststream.nim
index 2ce9a0e8..6c1bbc3c 100644
--- a/tests/teststream.nim
+++ b/tests/teststream.nim
@@ -8,6 +8,8 @@
 import strutils, unittest, os
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 when defined(windows):
   import winlean
 else:
diff --git a/tests/testsync.nim b/tests/testsync.nim
index 02b94332..56c6a77b 100644
--- a/tests/testsync.nim
+++ b/tests/testsync.nim
@@ -8,6 +8,8 @@
 import unittest
 import ../chronos
 
+when defined(nimHasUsed): {.used.}
+
 suite "Asynchronous sync primitives test suite":
   var testLockResult = ""
   var testEventResult = ""
diff --git a/tests/testtime.nim b/tests/testtime.nim
index 00401d9b..56649e3e 100644
--- a/tests/testtime.nim
+++ b/tests/testtime.nim
@@ -8,6 +8,8 @@
 import os, unittest
 import ../chronos, ../chronos/timer
 
+when defined(nimHasUsed): {.used.}
+
 suite "Asynchronous timers test suite":
   const TimersCount = 10