diff --git a/amazon-kinesis-client/src/main/java/software/amazon/kinesis/coordinator/Scheduler.java b/amazon-kinesis-client/src/main/java/software/amazon/kinesis/coordinator/Scheduler.java
index 9fa1d721..99de1ebd 100644
--- a/amazon-kinesis-client/src/main/java/software/amazon/kinesis/coordinator/Scheduler.java
+++ b/amazon-kinesis-client/src/main/java/software/amazon/kinesis/coordinator/Scheduler.java
@@ -122,6 +122,8 @@ public class Scheduler implements Runnable {
     private volatile long shutdownStartTimeMillis;
     private volatile boolean shutdownComplete = false;
 
+    private final Object lock = new Object();
+
     /**
      * Used to ensure that only one requestedShutdown is in progress at a time.
      */
@@ -222,55 +224,57 @@ public class Scheduler implements Runnable {
     }
 
     private void initialize() {
-        workerStateChangeListener.onWorkerStateChange(WorkerStateChangeListener.WorkerState.INITIALIZING);
-        boolean isDone = false;
-        Exception lastException = null;
+        synchronized (lock) {
+            workerStateChangeListener.onWorkerStateChange(WorkerStateChangeListener.WorkerState.INITIALIZING);
+            boolean isDone = false;
+            Exception lastException = null;
 
-        for (int i = 0; (!isDone) && (i < maxInitializationAttempts); i++) {
-            try {
-                log.info("Initialization attempt {}", (i + 1));
-                log.info("Initializing LeaseCoordinator");
-                leaseCoordinator.initialize();
+            for (int i = 0; (!isDone) && (i < maxInitializationAttempts); i++) {
+                try {
+                    log.info("Initialization attempt {}", (i + 1));
+                    log.info("Initializing LeaseCoordinator");
+                    leaseCoordinator.initialize();
 
-                TaskResult result = null;
-                if (!skipShardSyncAtWorkerInitializationIfLeasesExist || leaseRefresher.isLeaseTableEmpty()) {
-                    log.info("Syncing Kinesis shard info");
-                    ShardSyncTask shardSyncTask = new ShardSyncTask(shardDetector, leaseRefresher, initialPosition,
-                            cleanupLeasesUponShardCompletion, ignoreUnexpetedChildShards, 0L, metricsFactory);
-                    result = new MetricsCollectingTaskDecorator(shardSyncTask, metricsFactory).call();
-                } else {
-                    log.info("Skipping shard sync per configuration setting (and lease table is not empty)");
-                }
-
-                if (result == null || result.getException() == null) {
-                    if (!leaseCoordinator.isRunning()) {
-                        log.info("Starting LeaseCoordinator");
-                        leaseCoordinator.start();
+                    TaskResult result = null;
+                    if (!skipShardSyncAtWorkerInitializationIfLeasesExist || leaseRefresher.isLeaseTableEmpty()) {
+                        log.info("Syncing Kinesis shard info");
+                        ShardSyncTask shardSyncTask = new ShardSyncTask(shardDetector, leaseRefresher, initialPosition,
+                                cleanupLeasesUponShardCompletion, ignoreUnexpetedChildShards, 0L, metricsFactory);
+                        result = new MetricsCollectingTaskDecorator(shardSyncTask, metricsFactory).call();
                     } else {
-                        log.info("LeaseCoordinator is already running. No need to start it.");
+                        log.info("Skipping shard sync per configuration setting (and lease table is not empty)");
                     }
-                    isDone = true;
-                } else {
-                    lastException = result.getException();
+
+                    if (result == null || result.getException() == null) {
+                        if (!leaseCoordinator.isRunning()) {
+                            log.info("Starting LeaseCoordinator");
+                            leaseCoordinator.start();
+                        } else {
+                            log.info("LeaseCoordinator is already running. No need to start it.");
+                        }
+                        isDone = true;
+                    } else {
+                        lastException = result.getException();
+                    }
+                } catch (LeasingException e) {
+                    log.error("Caught exception when initializing LeaseCoordinator", e);
+                    lastException = e;
+                } catch (Exception e) {
+                    lastException = e;
+                }
+
+                try {
+                    Thread.sleep(parentShardPollIntervalMillis);
+                } catch (InterruptedException e) {
+                    log.debug("Sleep interrupted while initializing worker.");
                 }
-            } catch (LeasingException e) {
-                log.error("Caught exception when initializing LeaseCoordinator", e);
-                lastException = e;
-            } catch (Exception e) {
-                lastException = e;
             }
 
-            try {
-                Thread.sleep(parentShardPollIntervalMillis);
-            } catch (InterruptedException e) {
-                log.debug("Sleep interrupted while initializing worker.");
+            if (!isDone) {
+                throw new RuntimeException(lastException);
             }
+            workerStateChangeListener.onWorkerStateChange(WorkerStateChangeListener.WorkerState.STARTED);
         }
-
-        if (!isDone) {
-            throw new RuntimeException(lastException);
-        }
-        workerStateChangeListener.onWorkerStateChange(WorkerStateChangeListener.WorkerState.STARTED);
     }
 
     @VisibleForTesting
@@ -463,21 +467,23 @@ public class Scheduler implements Runnable {
      * </ol>
      */
     public void shutdown() {
-        if (shutdown) {
-            log.warn("Shutdown requested a second time.");
-            return;
+        synchronized (lock) {
+            if (shutdown) {
+                log.warn("Shutdown requested a second time.");
+                return;
+            }
+            log.info("Worker shutdown requested.");
+
+            // Set shutdown flag, so Worker.run can start shutdown process.
+            shutdown = true;
+            shutdownStartTimeMillis = System.currentTimeMillis();
+
+            // Stop lease coordinator, so leases are not renewed or stolen from other workers.
+            // Lost leases will force Worker to begin shutdown process for all shard consumers in
+            // Worker.run().
+            leaseCoordinator.stop();
+            workerStateChangeListener.onWorkerStateChange(WorkerStateChangeListener.WorkerState.SHUT_DOWN);
         }
-        log.info("Worker shutdown requested.");
-
-        // Set shutdown flag, so Worker.run can start shutdown process.
-        shutdown = true;
-        shutdownStartTimeMillis = System.currentTimeMillis();
-
-        // Stop lease coordinator, so leases are not renewed or stolen from other workers.
-        // Lost leases will force Worker to begin shutdown process for all shard consumers in
-        // Worker.run().
-        leaseCoordinator.stop();
-        workerStateChangeListener.onWorkerStateChange(WorkerStateChangeListener.WorkerState.SHUT_DOWN);
     }
 
     /**