diff --git a/arduino-core/src/cc/arduino/packages/discoverers/serial/SerialBoardsLister.java b/arduino-core/src/cc/arduino/packages/discoverers/serial/SerialBoardsLister.java
index b4ac2da9dc4..4de3626f612 100644
--- a/arduino-core/src/cc/arduino/packages/discoverers/serial/SerialBoardsLister.java
+++ b/arduino-core/src/cc/arduino/packages/discoverers/serial/SerialBoardsLister.java
@@ -54,7 +54,7 @@ public void start(Timer timer) {
     timer.schedule(this, 0, 1000);
   }
 
-  public void retriggerDiscovery() {
+  public synchronized void retriggerDiscovery() {
     while (BaseNoGui.packages == null) {
       try {
         Thread.sleep(1000);