diff --git a/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClusterCleanupOnShutdown.java b/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClusterCleanupOnShutdown.java
index 0381cece108..79f13198388 100644
--- a/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClusterCleanupOnShutdown.java
+++ b/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClusterCleanupOnShutdown.java
@@ -19,16 +19,12 @@ public class TestClusterCleanupOnShutdown implements Runnable {
 
     private Set<ElasticsearchCluster> clustersToWatch = new HashSet<>();
 
-    public void watch(Collection<ElasticsearchCluster> cluster) {
-        synchronized (clustersToWatch) {
-            clustersToWatch.addAll(clustersToWatch);
-        }
+    public synchronized void watch(Collection<ElasticsearchCluster> clusters) {
+        clustersToWatch.addAll(clusters);
     }
 
-    public void unWatch(Collection<ElasticsearchCluster> cluster) {
-        synchronized (clustersToWatch) {
-            clustersToWatch.removeAll(clustersToWatch);
-        }
+    public synchronized void unWatch(Collection<ElasticsearchCluster> clusters) {
+        clustersToWatch.removeAll(clusters);
     }
 
     @Override
@@ -38,21 +34,23 @@ public class TestClusterCleanupOnShutdown implements Runnable {
                 Thread.sleep(Long.MAX_VALUE);
             }
         } catch (InterruptedException interrupted) {
-            synchronized (clustersToWatch) {
-                if (clustersToWatch.isEmpty()) {
-                    return;
-                }
-                logger.info("Cleanup thread was interrupted, shutting down all clusters");
-                Iterator<ElasticsearchCluster> iterator = clustersToWatch.iterator();
-                while (iterator.hasNext()) {
-                    ElasticsearchCluster cluster = iterator.next();
-                    iterator.remove();
-                    try {
-                        cluster.stop(false);
-                    } catch (Exception e) {
-                        logger.warn("Could not shut down {}", cluster, e);
-                    }
-                }
+            shutdownClusters();
+        }
+    }
+
+    public synchronized void shutdownClusters() {
+        if (clustersToWatch.isEmpty()) {
+            return;
+        }
+        logger.info("Cleanup thread was interrupted, shutting down all clusters");
+        Iterator<ElasticsearchCluster> iterator = clustersToWatch.iterator();
+        while (iterator.hasNext()) {
+            ElasticsearchCluster cluster = iterator.next();
+            iterator.remove();
+            try {
+                cluster.stop(false);
+            } catch (Exception e) {
+                logger.warn("Could not shut down {}", cluster, e);
             }
         }
     }
diff --git a/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClustersCleanupExtension.java b/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClustersCleanupExtension.java
index 14bdfa952db..86d496358c1 100644
--- a/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClustersCleanupExtension.java
+++ b/buildSrc/src/main/java/org/elasticsearch/gradle/testclusters/TestClustersCleanupExtension.java
@@ -33,7 +33,6 @@ public class TestClustersCleanupExtension {
         executorService.submit(cleanupThread);
     }
 
-
     public static void createExtension(Project project) {
         if (project.getRootProject().getExtensions().findByType(TestClustersCleanupExtension.class) != null) {
             return;
@@ -43,7 +42,7 @@ public class TestClustersCleanupExtension {
             "__testclusters_rate_limit",
             TestClustersCleanupExtension.class
         );
-        Thread shutdownHook = new Thread(ext.cleanupThread::run);
+        Thread shutdownHook = new Thread(ext.cleanupThread::shutdownClusters);
         Runtime.getRuntime().addShutdownHook(shutdownHook);
         project.getGradle().buildFinished(buildResult -> {
             ext.executorService.shutdownNow();