diff --git a/testing/agent/src/main/java/sbt/ForkMain.java b/testing/agent/src/main/java/sbt/ForkMain.java
index 24acaf52b..a92d02506 100644
--- a/testing/agent/src/main/java/sbt/ForkMain.java
+++ b/testing/agent/src/main/java/sbt/ForkMain.java
@@ -17,6 +17,7 @@ import java.net.Socket;
 import java.net.InetAddress;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.List;
 import java.util.concurrent.*;
 
@@ -294,7 +295,7 @@ final public class ForkMain {
 					Task[] nestedTasks;
 					final TaskDef taskDef = task.taskDef();
 					try {
-						final List<ForkEvent> eventList = new ArrayList<ForkEvent>();
+						final Collection<ForkEvent> eventList = new ConcurrentLinkedDeque<ForkEvent>();
 						final EventHandler handler = new EventHandler() { public void handle(final Event e){ eventList.add(new ForkEvent(e)); } };
 						logDebug(os, "  Running " + taskDef);
 						nestedTasks = task.execute(handler, loggers);