diff --git a/vendor.conf b/vendor.conf
index a740458cbf..bfbd4aac36 100644
--- a/vendor.conf
+++ b/vendor.conf
@@ -101,7 +101,7 @@ github.com/docker/containerd 595e75c212d19a81d2b808a518fe1afc1391dad5
 github.com/tonistiigi/fifo 1405643975692217d6720f8b54aeee1bf2cd5cf4
 
 # cluster
-github.com/docker/swarmkit f93948cb430facd540e3c65c606384a89b3ac40f
+github.com/docker/swarmkit 17756457ad6dc4d8a639a1f0b7a85d1b65a617bb
 github.com/golang/mock bd3c8e81be01eef76d4b503f5e687d2d1354d2d9
 github.com/gogo/protobuf v0.3
 github.com/cloudflare/cfssl 7fb22c8cba7ecaf98e4082d22d65800cf45e042a
diff --git a/vendor/github.com/docker/swarmkit/manager/scheduler/scheduler.go b/vendor/github.com/docker/swarmkit/manager/scheduler/scheduler.go
index c32d3c44a4..a1a8d9cc25 100644
--- a/vendor/github.com/docker/swarmkit/manager/scheduler/scheduler.go
+++ b/vendor/github.com/docker/swarmkit/manager/scheduler/scheduler.go
@@ -1,7 +1,6 @@
 package scheduler
 
 import (
-	"container/list"
 	"time"
 
 	"github.com/docker/swarmkit/api"
@@ -30,7 +29,7 @@ type schedulingDecision struct {
 // Scheduler assigns tasks to nodes.
 type Scheduler struct {
 	store           *store.MemoryStore
-	unassignedTasks *list.List
+	unassignedTasks map[string]*api.Task
 	// preassignedTasks already have NodeID, need resource validation
 	preassignedTasks map[string]*api.Task
 	nodeSet          nodeSet
@@ -47,7 +46,7 @@ type Scheduler struct {
 func New(store *store.MemoryStore) *Scheduler {
 	return &Scheduler{
 		store:            store,
-		unassignedTasks:  list.New(),
+		unassignedTasks:  make(map[string]*api.Task),
 		preassignedTasks: make(map[string]*api.Task),
 		allTasks:         make(map[string]*api.Task),
 		stopChan:         make(chan struct{}),
@@ -191,7 +190,7 @@ func (s *Scheduler) Stop() {
 
 // enqueue queues a task for scheduling.
 func (s *Scheduler) enqueue(t *api.Task) {
-	s.unassignedTasks.PushBack(t)
+	s.unassignedTasks[t.ID] = t
 }
 
 func (s *Scheduler) createTask(ctx context.Context, t *api.Task) int {
@@ -333,15 +332,12 @@ func (s *Scheduler) processPreassignedTasks(ctx context.Context) {
 // tick attempts to schedule the queue.
 func (s *Scheduler) tick(ctx context.Context) {
 	tasksByCommonSpec := make(map[string]map[string]*api.Task)
-	schedulingDecisions := make(map[string]schedulingDecision, s.unassignedTasks.Len())
+	schedulingDecisions := make(map[string]schedulingDecision, len(s.unassignedTasks))
 
-	var next *list.Element
-	for e := s.unassignedTasks.Front(); e != nil; e = next {
-		next = e.Next()
-		t := s.allTasks[e.Value.(*api.Task).ID]
+	for taskID, t := range s.unassignedTasks {
 		if t == nil || t.NodeID != "" {
 			// task deleted or already assigned
-			s.unassignedTasks.Remove(e)
+			delete(s.unassignedTasks, taskID)
 			continue
 		}
 
@@ -362,8 +358,8 @@ func (s *Scheduler) tick(ctx context.Context) {
 		if tasksByCommonSpec[taskGroupKey] == nil {
 			tasksByCommonSpec[taskGroupKey] = make(map[string]*api.Task)
 		}
-		tasksByCommonSpec[taskGroupKey][t.ID] = t
-		s.unassignedTasks.Remove(e)
+		tasksByCommonSpec[taskGroupKey][taskID] = t
+		delete(s.unassignedTasks, taskID)
 	}
 
 	for _, taskGroup := range tasksByCommonSpec {
@@ -540,6 +536,12 @@ func (s *Scheduler) scheduleTaskGroup(ctx context.Context, taskGroup map[string]
 	failedConstraints := make(map[int]bool) // key is index in nodes slice
 	nodeIter := 0
 	for taskID, t := range taskGroup {
+		// Skip tasks which were already scheduled because they ended
+		// up in two groups at once.
+		if _, exists := schedulingDecisions[taskID]; exists {
+			continue
+		}
+
 		n := &nodes[nodeIter%len(nodes)]
 
 		log.G(ctx).WithField("task.id", t.ID).Debugf("assigning to node %s", n.ID)