diff --git a/libp2p/connection.nim b/libp2p/connection.nim
index ae47d0439..64b3066fe 100644
--- a/libp2p/connection.nim
+++ b/libp2p/connection.nim
@@ -15,7 +15,7 @@ import peerinfo,
        varint,
        vbuffer
 
-const DefaultReadSize*: uint = 1 shl 20 # 1mb, in order to fit mplex spec
+const DefaultReadSize* = 1 shl 20
 
 type
   Connection* = ref object of LPStream
@@ -24,10 +24,14 @@ type
     observedAddrs*: Multiaddress
 
   InvalidVarintException = object of LPStreamError
+  InvalidVarintSizeException = object of LPStreamError
 
 proc newInvalidVarintException*(): ref InvalidVarintException =
   newException(InvalidVarintException, "unable to parse varint")
 
+proc newInvalidVarintSizeException*(): ref InvalidVarintSizeException =
+  newException(InvalidVarintSizeException, "wrong varint size")
+
 proc init*[T: Connection](self: var T, stream: LPStream) =
   ## create a new Connection for the specified async reader/writer
   new self
@@ -124,8 +128,8 @@ proc readLp*(s: Connection): Future[seq[byte]] {.async, gcsafe.} =
         break
     if res != VarintStatus.Success:
       raise newInvalidVarintException()
-    if size > DefaultReadSize:
-      raise newLPStreamLimitError()
+    if size.int > DefaultReadSize:
+      raise newInvalidVarintSizeException()
     buff.setLen(size)
     if size > 0.uint:
       trace "reading exact bytes from stream", size = size
diff --git a/libp2p/muxers/mplex/coder.nim b/libp2p/muxers/mplex/coder.nim
index 0451805d4..9f8ee9ee3 100644
--- a/libp2p/muxers/mplex/coder.nim
+++ b/libp2p/muxers/mplex/coder.nim
@@ -7,7 +7,7 @@
 ## This file may not be copied, modified, or distributed except according to
 ## those terms.
 
-import chronos, options
+import chronos
 import nimcrypto/utils, chronicles
 import types,
        ../../connection,
@@ -18,30 +18,35 @@ import types,
 logScope:
   topic = "MplexCoder"
 
+const DefaultChannelSize* = 1 shr 20
+
 type
   Msg* = tuple
     id: uint
     msgType: MessageType
     data: seq[byte]
 
-proc readMplexVarint(conn: Connection): Future[Option[uint]] {.async, gcsafe.} =
+proc readMplexVarint(conn: Connection): Future[uint] {.async, gcsafe.} =
   var
     varint: uint
     length: int
     res: VarintStatus
     buffer = newSeq[byte](10)
 
-  result = none(uint)
   try:
     for i in 0..<len(buffer):
       await conn.readExactly(addr buffer[i], 1)
       res = PB.getUVarint(buffer.toOpenArray(0, i), length, varint)
       if res == VarintStatus.Success:
-        return some(varint)
+        break
     if res != VarintStatus.Success:
       raise newInvalidVarintException()
+    if varint.int > DefaultReadSize:
+      raise newInvalidVarintSizeException()
+    return varint
   except LPStreamIncompleteError as exc:
     trace "unable to read varint", exc = exc.msg
+    raise exc
 
 proc readMsg*(conn: Connection): Future[Msg] {.async, gcsafe.} =
   let headerVarint = await conn.readMplexVarint()