diff --git a/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/HttpTunnelServer.java b/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/HttpTunnelServer.java
index 829e87bf5f..fe1ee9673c 100644
--- a/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/HttpTunnelServer.java
+++ b/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/tunnel/server/HttpTunnelServer.java
@@ -274,8 +274,8 @@ public class HttpTunnelServer {
 		}
 
 		private void closeStaleHttpConnections() throws IOException {
-			checkNotDisconnected();
 			synchronized (this.httpConnections) {
+				checkNotDisconnected();
 				Iterator<HttpConnection> iterator = this.httpConnections.iterator();
 				while (iterator.hasNext()) {
 					HttpConnection httpConnection = iterator.next();