diff --git a/quic/api.nim b/quic/api.nim
index 541fb91..8825b14 100644
--- a/quic/api.nim
+++ b/quic/api.nim
@@ -102,10 +102,7 @@ proc listen*(
 proc dial*(
     self: QuicClient, address: TransportAddress
 ): Future[Connection] {.
-    async: (
-      raises:
-        [CancelledError, CatchableError, TimeOutError, QuicError, TransportOsError]
-    )
+    async: (raises: [CancelledError, TimeOutError, QuicError, TransportOsError])
 .} =
   let tlsBackend = newClientTLSBackend(
     self.tlsConfig.certificate, self.tlsConfig.key, self.tlsConfig.alpn,
@@ -124,12 +121,19 @@ proc dial*(
 
   let udp = newDatagramTransport(onReceive)
   connection = newOutgoingConnection(tlsBackend, udp, address, self.rng)
+
   try:
     connection.startHandshake()
     await connection.waitForHandshake()
-  except CatchableError as exc:
-    # whatever error happens we need to destroy tlsBackend to free resources
+  # whatever error happens we need to destroy tlsBackend to free resources
+  except CancelledError as e:
     tlsBackend.destroy()
-    raise exc
+    raise e
+  except TimeOutError as e:
+    tlsBackend.destroy()
+    raise e
+  except QuicError as e:
+    tlsBackend.destroy()
+    raise e
 
   return connection
diff --git a/quic/connection.nim b/quic/connection.nim
index 442ce21..55b0242 100644
--- a/quic/connection.nim
+++ b/quic/connection.nim
@@ -42,11 +42,11 @@ proc `onRemoveId=`*(connection: Connection, callback: IdCallback) =
 proc `onClose=`*(connection: Connection, callback: proc() {.gcsafe, raises: [].}) =
   connection.onClose = Opt.some(callback)
 
-proc drop*(connection: Connection) {.async.} =
+proc drop*(connection: Connection) {.async: (raises: [CancelledError, QuicError]).} =
   trace "Dropping connection"
   await connection.quic.drop()
 
-proc close*(connection: Connection) {.async.} =
+proc close*(connection: Connection) {.async: (raises: [CancelledError, QuicError]).} =
   await connection.quic.close()
   if connection is OutgoingConnection:
     let outConn = OutgoingConnection(connection)
@@ -54,7 +54,7 @@ proc close*(connection: Connection) {.async.} =
       outConn.tlsBackend.get().destroy()
       outConn.tlsBackend = Opt.none(TLSBackend)
 
-proc waitClosed*(connection: Connection) {.async.} =
+proc waitClosed*(connection: Connection) {.async: (raises: [CancelledError]).} =
   await connection.closed.wait()
   if connection is OutgoingConnection:
     let outConn = OutgoingConnection(connection)
@@ -81,7 +81,7 @@ proc startSending(connection: Connection, remote: TransportAddress) =
 
   connection.loop = asyncLoop(send)
 
-proc stopSending(connection: Connection) {.async.} =
+proc stopSending(connection: Connection) {.async: (raises: [CancelledError]).} =
   trace "Stopping sending loop"
   await connection.loop.cancelAndWait()
 
@@ -91,7 +91,7 @@ method closeUdp(connection: Connection) {.async: (raises: []), base.} =
 method closeUdp(connection: OutgoingConnection) {.async: (raises: []).} =
   await connection.udp.closeWait()
 
-proc disconnect(connection: Connection) {.async.} =
+proc disconnect(connection: Connection) {.async: (raises: [CancelledError]).} =
   trace "Disconnecting connection"
   await connection.stopSending()
   await connection.closeUdp()
@@ -111,7 +111,7 @@ proc newIncomingConnection*(
     newQuicServerConnection(tlsBackend, udp.localAddress, remote, datagram, rng)
   let closed = newAsyncEvent()
   let connection = IncomingConnection(udp: udp, quic: quic, closed: closed)
-  proc onDisconnect() {.async.} =
+  proc onDisconnect() {.async: (raises: [CancelledError]).} =
     trace "Calling onDisconnect for newIncomingConnection"
     await connection.disconnect()
 
@@ -120,7 +120,9 @@ proc newIncomingConnection*(
   connection.startSending(remote)
   connection
 
-proc ensureClosed(connection: Connection) {.async.} =
+proc ensureClosed(
+    connection: Connection
+) {.async: (raises: [CancelledError, QuicError]).} =
   ## This will automatically close the connection if there's an idle timeout reported
   ## by ngtcp2
   discard await race(connection.quic.timeout.wait(), connection.closed.wait())
@@ -137,7 +139,7 @@ proc newOutgoingConnection*(
   let connection = OutgoingConnection(
     udp: udp, quic: quic, closed: closed, tlsBackend: Opt.some(tlsBackend)
   )
-  proc onDisconnect() {.async.} =
+  proc onDisconnect() {.async: (raises: [CancelledError]).} =
     trace "Calling onDisconnect for newOutgoingConnection"
     await connection.disconnect()
 
@@ -154,7 +156,7 @@ proc startHandshake*(connection: Connection) {.gcsafe.} =
 
 proc waitForHandshake*(
     connection: Connection
-) {.async: (raises: [CancelledError, TimeOutError, CatchableError]).} =
+) {.async: (raises: [CancelledError, QuicError, TimeOutError]).} =
   let key = connection.quic.error.register()
   defer:
     connection.quic.error.unregister(key)
@@ -178,14 +180,22 @@ proc waitForHandshake*(
     errFut.cancelSoon()
     handshakeFut.cancelSoon()
     await connCloseFut
-    raise newException(TimeOutError, "handshake timed out")
+    raise newException(TimeOutError, "connection handshake timed out")
   elif raceFut == errFut:
     let connCloseFut = connection.close()
     timeoutFut.cancelSoon()
     handshakeFut.cancelSoon()
     await connCloseFut
-    let err = await errFut
-    raise newException(QuicError, "connection error: " & err[0])
+
+    let err =
+      try:
+        await errFut
+      except AsyncEventQueueFullError as e:
+        raise newException(
+          QuicError, "connection handshake error: waiting on error: " & e.msg
+        )
+
+    raise newException(QuicError, "connection handshake error: " & err[0])
   else:
     errFut.cancelSoon()
     timeoutFut.cancelSoon()
diff --git a/quic/listener.nim b/quic/listener.nim
index f965cc7..6eea35d 100644
--- a/quic/listener.nim
+++ b/quic/listener.nim
@@ -88,15 +88,19 @@ proc newListener*(
   listener.udp = newDatagramTransport(onReceive, local = address)
   listener
 
-proc waitForIncoming*(listener: Listener): Future[Connection] {.async.} =
+proc waitForIncoming*(
+    listener: Listener
+): Future[Connection] {.async: (raises: [CancelledError]).} =
   await listener.incoming.get()
 
-proc accept*(listener: Listener): Future[Connection] {.async.} =
+proc accept*(
+    listener: Listener
+): Future[Connection] {.async: (raises: [CancelledError, QuicError, TimeOutError]).} =
   let conn = await listener.waitForIncoming()
   await conn.waitForHandshake()
   return conn
 
-proc stop*(listener: Listener) {.async.} =
+proc stop*(listener: Listener) {.async: (raises: [CancelledError]).} =
   await listener.udp.closeWait()
 
 proc destroy*(listener: Listener) =
diff --git a/quic/transport/ngtcp2/connstate/disconnectingstate.nim b/quic/transport/ngtcp2/connstate/disconnectingstate.nim
index 313f8de..494b6e4 100644
--- a/quic/transport/ngtcp2/connstate/disconnectingstate.nim
+++ b/quic/transport/ngtcp2/connstate/disconnectingstate.nim
@@ -11,7 +11,7 @@ logScope:
 
 type DisconnectingConnection* = ref object of ConnectionState
   connection: Opt[QuicConnection]
-  disconnect: Future[void]
+  disconnect: Future[void].Raising([CancelledError, QuicError])
   ids: seq[ConnectionId]
 
 proc newDisconnectingConnection*(
@@ -19,7 +19,9 @@ proc newDisconnectingConnection*(
 ): DisconnectingConnection =
   DisconnectingConnection(ids: ids, derCertificates: certificates)
 
-proc callDisconnect(connection: QuicConnection) {.async.} =
+proc callDisconnect(
+    connection: QuicConnection
+) {.async: (raises: [CancelledError, QuicError]).} =
   let disconnect = connection.disconnect.valueOr:
     return
   trace "Calling disconnect proc on QuicConnection"
@@ -55,21 +57,10 @@ method openStream(
 ): Future[Stream] {.async: (raises: [CancelledError, QuicError]).} =
   raise newException(ClosedConnectionError, "connection is disconnecting")
 
-template handleWithQuicError*(body: untyped) =
-  try:
-    body
-  except CancelledError as e:
-    raise e
-  except QuicError as e:
-    raise e
-  except CatchableError as e:
-    raise newException(QuicError, e.msg)
-
 method close(
     state: DisconnectingConnection
 ) {.async: (raises: [CancelledError, QuicError]).} =
-  handleWithQuicError:
-    await state.disconnect
+  await state.disconnect
   let connection = state.connection.valueOr:
     return
   connection.switch(newClosedConnection(state.derCertificates))
@@ -78,8 +69,7 @@ method drop(
     state: DisconnectingConnection
 ) {.async: (raises: [CancelledError, QuicError]).} =
   trace "Drop DisconnectingConnection state"
-  handleWithQuicError:
-    await state.disconnect
+  await state.disconnect
   let connection = state.connection.valueOr:
     return
   connection.switch(newClosedConnection(state.derCertificates))
diff --git a/quic/transport/quicconnection.nim b/quic/transport/quicconnection.nim
index 751f5df..674ef6e 100644
--- a/quic/transport/quicconnection.nim
+++ b/quic/transport/quicconnection.nim
@@ -14,7 +14,7 @@ type
     handshake*: AsyncEvent
     timeout*: AsyncEvent
     error*: AsyncEventQueue[string]
-    disconnect*: Opt[proc(): Future[void] {.gcsafe, raises: [].}]
+    disconnect*: Opt[proc(): Future[void] {.gcsafe, async: (raises: [CancelledError]).}]
     onNewId*: IdCallback
     onRemoveId*: IdCallback
 
diff --git a/quic/transport/stream.nim b/quic/transport/stream.nim
index 46719b8..eef6533 100644
--- a/quic/transport/stream.nim
+++ b/quic/transport/stream.nim
@@ -76,25 +76,32 @@ proc switch*(stream: Stream, newState: StreamState) {.raises: [QuicError].} =
 proc id*(stream: Stream): int64 =
   stream.id
 
-proc read*(stream: Stream): Future[seq[byte]] {.async.} =
+proc read*(
+    stream: Stream
+): Future[seq[byte]] {.async: (raises: [CancelledError, QuicError]).} =
   result = await stream.state.read()
 
-proc write*(stream: Stream, bytes: seq[byte]) {.async.} =
+proc write*(
+    stream: Stream, bytes: seq[byte]
+) {.async: (raises: [CancelledError, QuicError]).} =
   # Writing has to be serialized on the same stream as otherwise
   # data might not be sent correctly.
   await stream.lock.acquire()
   defer:
-    stream.lock.release()
+    try:
+      stream.lock.release()
+    except AsyncLockError:
+      discard # should not happen - lock acquired directly above
 
   await stream.state.write(bytes)
 
-proc close*(stream: Stream) {.async.} =
+proc close*(stream: Stream) {.async: (raises: [CancelledError, QuicError]).} =
   await stream.state.close()
 
-proc closeWrite*(stream: Stream) {.async.} =
+proc closeWrite*(stream: Stream) {.async: (raises: [CancelledError, QuicError]).} =
   await stream.state.closeWrite()
 
-proc closeRead*(stream: Stream) {.async.} =
+proc closeRead*(stream: Stream) {.async: (raises: [CancelledError, QuicError]).} =
   await stream.state.closeRead()
 
 proc reset*(stream: Stream) =