diff --git a/spring-integration-ftp/src/test/java/org/springframework/integration/ftp/inbound/RotatingServersTests.java b/spring-integration-ftp/src/test/java/org/springframework/integration/ftp/inbound/RotatingServersTests.java
index 661c382de7..43d50a7a1f 100644
--- a/spring-integration-ftp/src/test/java/org/springframework/integration/ftp/inbound/RotatingServersTests.java
+++ b/spring-integration-ftp/src/test/java/org/springframework/integration/ftp/inbound/RotatingServersTests.java
@@ -22,6 +22,7 @@ import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
@@ -168,7 +169,7 @@ public class RotatingServersTests extends FtpTestSupport {
 
 		private final CountDownLatch latch = new CountDownLatch(17);
 
-		List<Integer> sessionSources = new ArrayList<>();
+		final List<Integer> sessionSources = new CopyOnWriteArrayList<>();
 
 		@Bean
 		public SessionFactory<FTPFile> factory1() {