diff --git a/chronos/streams/asyncstream.nim b/chronos/streams/asyncstream.nim
index 6fc194fa..bc1f6f94 100644
--- a/chronos/streams/asyncstream.nim
+++ b/chronos/streams/asyncstream.nim
@@ -289,6 +289,12 @@ proc readExactly*(rstream: AsyncStreamReader, pbytes: pointer,
   ##
   ## If EOF is received and ``nbytes`` is not yet readed, the procedure
   ## will raise ``AsyncStreamIncompleteError``.
+  doAssert(not(isNil(pbytes)), "pbytes must not be nil")
+  doAssert(nbytes >= 0, "nbytes must be non-negative integer")
+
+  if nbytes == 0:
+    return
+
   if not rstream.running():
     raise newAsyncStreamIncorrectError("Incorrect stream state")
 
@@ -329,6 +335,9 @@ proc readOnce*(rstream: AsyncStreamReader, pbytes: pointer,
   ##
   ## If internal buffer is not empty, ``nbytes`` bytes will be transferred from
   ## internal buffer, otherwise it will wait until some bytes will be received.
+  doAssert(not(isNil(pbytes)), "pbytes must not be nil")
+  doAssert(nbytes > 0, "nbytes must be positive value")
+
   if not rstream.running():
     raise newAsyncStreamIncorrectError("Incorrect stream state")
 
@@ -374,6 +383,13 @@ proc readUntil*(rstream: AsyncStreamReader, pbytes: pointer, nbytes: int,
   ## will raise ``AsyncStreamLimitError``.
   ##
   ## Procedure returns actual number of bytes read.
+  doAssert(not(isNil(pbytes)), "pbytes must not be nil")
+  doAssert(len(sep) > 0, "separator must not be empty")
+  doAssert(nbytes >= 0, "nbytes must be non-negative value")
+
+  if nbytes == 0:
+    raise newAsyncStreamLimitError()
+
   if not rstream.running():
     raise newAsyncStreamIncorrectError("Incorrect stream state")
 
diff --git a/chronos/transports/stream.nim b/chronos/transports/stream.nim
index 59d89da1..45073e11 100644
--- a/chronos/transports/stream.nim
+++ b/chronos/transports/stream.nim
@@ -1998,11 +1998,20 @@ template readLoop(name, body: untyped): untyped =
 proc readExactly*(transp: StreamTransport, pbytes: pointer,
                   nbytes: int) {.async.} =
   ## Read exactly ``nbytes`` bytes from transport ``transp`` and store it to
-  ## ``pbytes``.
+  ## ``pbytes``. ``pbytes`` must not be ``nil`` pointer and ``nbytes`` should
+  ## be Natural.
+  ##
+  ## If ``nbytes == 0`` this operation will return immediately.
   ##
   ## If EOF is received and ``nbytes`` is not yet readed, the procedure
   ## will raise ``TransportIncompleteError``, potentially with some bytes
   ## already written.
+  doAssert(not(isNil(pbytes)), "pbytes must not be nil")
+  doAssert(nbytes >= 0, "nbytes must be non-negative integer")
+
+  if nbytes == 0:
+    return
+
   var index = 0
   var pbuffer = cast[ptr UncheckedArray[byte]](pbytes)
   readLoop("stream.transport.readExactly"):
@@ -2021,6 +2030,9 @@ proc readOnce*(transp: StreamTransport, pbytes: pointer,
   ##
   ## If internal buffer is not empty, ``nbytes`` bytes will be transferred from
   ## internal buffer, otherwise it will wait until some bytes will be received.
+  doAssert(not(isNil(pbytes)), "pbytes must not be nil")
+  doAssert(nbytes > 0, "nbytes must be positive integer")
+
   var count = 0
   readLoop("stream.transport.readOnce"):
     if transp.offset == 0:
@@ -2045,6 +2057,13 @@ proc readUntil*(transp: StreamTransport, pbytes: pointer, nbytes: int,
   ## will raise ``TransportLimitError``.
   ##
   ## Procedure returns actual number of bytes read.
+  doAssert(not(isNil(pbytes)), "pbytes must not be nil")
+  doAssert(len(sep) > 0, "separator must not be empty")
+  doAssert(nbytes >= 0, "nbytes must be non-negative integer")
+
+  if nbytes == 0:
+    raise newException(TransportLimitError, "Limit reached!")
+
   var pbuffer = cast[ptr UncheckedArray[byte]](pbytes)
   var state = 0
   var k = 0