diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java
index f83b042..6d99ba7 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/impl/DistributedLockManager.java
@@ -33,7 +33,8 @@
 
     public static final String ONOS_LOCK_TABLE_NAME = "onos-locks";
 
-    private final ArrayListMultimap<String, LockRequest> locksToAcquire = ArrayListMultimap.create();
+    private final ArrayListMultimap<String, LockRequest> locksToAcquire = ArrayListMultimap
+            .create();
 
     @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
     private ClusterCommunicationService clusterCommunicator;
@@ -61,11 +62,7 @@
 
     @Override
     public Lock create(String path) {
-        return new DistributedLock(
-                path,
-                databaseService,
-                clusterService,
-                this);
+        return new DistributedLock(path, databaseService, clusterService, this);
     }
 
     @Override
@@ -80,21 +77,19 @@
         throw new UnsupportedOperationException();
     }
 
-    protected CompletableFuture<Void> lockIfAvailable(
-            Lock lock,
-            long waitTimeMillis,
-            int leaseDurationMillis) {
+    protected CompletableFuture<Void> lockIfAvailable(Lock lock,
+            long waitTimeMillis, int leaseDurationMillis) {
         CompletableFuture<Void> future = new CompletableFuture<>();
-        locksToAcquire.put(
-                lock.path(),
-                new LockRequest(lock, waitTimeMillis, leaseDurationMillis, future));
+        locksToAcquire.put(lock.path(), new LockRequest(lock, waitTimeMillis,
+                leaseDurationMillis, future));
         return future;
     }
 
     private class LockEventMessageListener implements ClusterMessageHandler {
         @Override
         public void handle(ClusterMessage message) {
-            TableModificationEvent event = DatabaseStateMachine.SERIALIZER.decode(message.payload());
+            TableModificationEvent event = DatabaseStateMachine.SERIALIZER
+                    .decode(message.payload());
             if (!event.tableName().equals(ONOS_LOCK_TABLE_NAME)) {
                 return;
             }
@@ -110,15 +105,20 @@
                     return;
                 }
 
-                Iterator<LockRequest> existingRequestIterator = existingRequests.iterator();
-                while (existingRequestIterator.hasNext()) {
-                    LockRequest request = existingRequestIterator.next();
-                    if (request.expirationTime().isAfter(DateTime.now())) {
-                        existingRequestIterator.remove();
-                    } else {
-                        if (request.lock().tryLock(request.leaseDurationMillis())) {
-                            request.future().complete(null);
-                            existingRequests.remove(0);
+                synchronized (existingRequests) {
+
+                    Iterator<LockRequest> existingRequestIterator = existingRequests
+                            .iterator();
+                    while (existingRequestIterator.hasNext()) {
+                        LockRequest request = existingRequestIterator.next();
+                        if (request.expirationTime().isAfter(DateTime.now())) {
+                            existingRequestIterator.remove();
+                        } else {
+                            if (request.lock().tryLock(
+                                    request.leaseDurationMillis())) {
+                                request.future().complete(null);
+                                existingRequestIterator.remove();
+                            }
                         }
                     }
                 }
@@ -133,14 +133,12 @@
         private final int leaseDurationMillis;
         private final CompletableFuture<Void> future;
 
-        public LockRequest(
-            Lock lock,
-            long waitTimeMillis,
-            int leaseDurationMillis,
-            CompletableFuture<Void> future) {
+        public LockRequest(Lock lock, long waitTimeMillis,
+                int leaseDurationMillis, CompletableFuture<Void> future) {
 
             this.lock = lock;
-            this.expirationTime = DateTime.now().plusMillis((int) waitTimeMillis);
+            this.expirationTime = DateTime.now().plusMillis(
+                    (int) waitTimeMillis);
             this.leaseDurationMillis = leaseDurationMillis;
             this.future = future;
         }