diff --git a/les/vflux/client/serverpool_test.go b/les/vflux/client/serverpool_test.go
index 763f72f03..c7d0245ef 100644
--- a/les/vflux/client/serverpool_test.go
+++ b/les/vflux/client/serverpool_test.go
@@ -63,7 +63,11 @@ type ServerPoolTest struct {
 	trusted              []string
 	waitCount, waitEnded int32
 
-	lock sync.Mutex
+	// preNegLock protects the cycle counter, testNodes list and its connected field
+	// (accessed from both the main thread and the preNeg callback)
+	preNegLock sync.Mutex
+	queryWg    *sync.WaitGroup // a new wait group is created each time the simulation is started
+	stopping   bool            // stopping avoid callind queryWg.Add after queryWg.Wait
 
 	cycle, conn, servedConn  int
 	serviceCycles, dialCount int
@@ -111,13 +115,21 @@ func (s *ServerPoolTest) addTrusted(i int) {
 
 func (s *ServerPoolTest) start() {
 	var testQuery QueryFunc
+	s.queryWg = new(sync.WaitGroup)
 	if s.preNeg {
 		testQuery = func(node *enode.Node) int {
+			s.preNegLock.Lock()
+			if s.stopping {
+				s.preNegLock.Unlock()
+				return 0
+			}
+			s.queryWg.Add(1)
 			idx := testNodeIndex(node.ID())
 			n := &s.testNodes[idx]
-			s.lock.Lock()
 			canConnect := !n.connected && n.connectCycles != 0 && s.cycle >= n.nextConnCycle
-			s.lock.Unlock()
+			s.preNegLock.Unlock()
+			defer s.queryWg.Done()
+
 			if s.preNegFail {
 				// simulate a scenario where UDP queries never work
 				s.beginWait()
@@ -181,11 +193,20 @@ func (s *ServerPoolTest) start() {
 }
 
 func (s *ServerPoolTest) stop() {
+	// disable further queries and wait if one is currently running
+	s.preNegLock.Lock()
+	s.stopping = true
+	s.preNegLock.Unlock()
+	s.queryWg.Wait()
+
 	quit := make(chan struct{})
 	s.quit <- quit
 	<-quit
 	s.sp.Stop()
 	s.spi.Close()
+	s.preNegLock.Lock()
+	s.stopping = false
+	s.preNegLock.Unlock()
 	for i := range s.testNodes {
 		n := &s.testNodes[i]
 		if n.connected {
@@ -205,7 +226,9 @@ func (s *ServerPoolTest) run() {
 				n := &s.testNodes[idx]
 				s.sp.UnregisterNode(n.node)
 				n.totalConn += s.cycle
+				s.preNegLock.Lock()
 				n.connected = false
+				s.preNegLock.Unlock()
 				n.node = nil
 				s.conn--
 				if n.service {
@@ -230,7 +253,9 @@ func (s *ServerPoolTest) run() {
 					s.servedConn++
 				}
 				n.totalConn -= s.cycle
+				s.preNegLock.Lock()
 				n.connected = true
+				s.preNegLock.Unlock()
 				dc := s.cycle + n.connectCycles
 				s.disconnect[dc] = append(s.disconnect[dc], idx)
 				n.node = dial
@@ -242,9 +267,9 @@ func (s *ServerPoolTest) run() {
 		}
 		s.serviceCycles += s.servedConn
 		s.clock.Run(time.Second)
-		s.lock.Lock()
+		s.preNegLock.Lock()
 		s.cycle++
-		s.lock.Unlock()
+		s.preNegLock.Unlock()
 	}
 }
 
@@ -255,11 +280,13 @@ func (s *ServerPoolTest) setNodes(count, conn, wait int, service, trusted bool)
 			idx = rand.Intn(spTestNodes)
 		}
 		res = append(res, idx)
+		s.preNegLock.Lock()
 		s.testNodes[idx] = spTestNode{
 			connectCycles: conn,
 			waitCycles:    wait,
 			service:       service,
 		}
+		s.preNegLock.Unlock()
 		if trusted {
 			s.addTrusted(idx)
 		}
@@ -273,7 +300,9 @@ func (s *ServerPoolTest) resetNodes() {
 			n.totalConn += s.cycle
 			s.sp.UnregisterNode(n.node)
 		}
+		s.preNegLock.Lock()
 		s.testNodes[i] = spTestNode{totalConn: n.totalConn}
+		s.preNegLock.Unlock()
 	}
 	s.conn, s.servedConn = 0, 0
 	s.disconnect = make(map[int][]int)
diff --git a/p2p/nodestate/nodestate.go b/p2p/nodestate/nodestate.go
index 9323d53cb..2af0d0a6b 100644
--- a/p2p/nodestate/nodestate.go
+++ b/p2p/nodestate/nodestate.go
@@ -808,7 +808,14 @@ func (ns *NodeStateMachine) addTimeout(n *enode.Node, mask bitMask, timeout time
 	ns.removeTimeouts(node, mask)
 	t := &nodeStateTimeout{mask: mask}
 	t.timer = ns.clock.AfterFunc(timeout, func() {
-		ns.SetState(n, Flags{}, Flags{mask: t.mask, setup: ns.setup}, 0)
+		ns.lock.Lock()
+		defer ns.lock.Unlock()
+
+		if !ns.opStart() {
+			return
+		}
+		ns.setState(n, Flags{}, Flags{mask: t.mask, setup: ns.setup}, 0)
+		ns.opFinish()
 	})
 	node.timeouts = append(node.timeouts, t)
 	if mask&ns.saveFlags != 0 {