diff --git a/sbt/src/sbt-test/tests/fork-async/build.sbt b/sbt/src/sbt-test/tests/fork-async/build.sbt
new file mode 100644
index 000000000..bb42b0c17
--- /dev/null
+++ b/sbt/src/sbt-test/tests/fork-async/build.sbt
@@ -0,0 +1,8 @@
+testFrameworks += new TestFramework("utest.runner.Framework")
+
+lazy val root = (project in file(".")).
+  settings(
+    scalaVersion := "2.12.4",
+    libraryDependencies += "com.lihaoyi" %% "utest" % "0.6.4" % Test,
+    fork in Test := true
+  )
diff --git a/sbt/src/sbt-test/tests/fork-async/src/test/scala/ForkAsyncTest.scala b/sbt/src/sbt-test/tests/fork-async/src/test/scala/ForkAsyncTest.scala
new file mode 100644
index 000000000..a8bc4c0f2
--- /dev/null
+++ b/sbt/src/sbt-test/tests/fork-async/src/test/scala/ForkAsyncTest.scala
@@ -0,0 +1,21 @@
+import utest._
+
+import utest._
+import utest.framework._
+
+import scala.concurrent.{ ExecutionContext, Promise }
+import scala.util.Success
+
+object ForkAsyncTest extends TestSuite {
+  val g = ExecutionContext.global
+  val n = 10
+  val (testNames, promises) = (1 to n).map(i => Tree(s"$i") -> Promise[Unit]).unzip
+  val testTrees = promises.zipWithIndex.map { case (p, i) =>
+    new TestCallTree(Left {
+      if (i == (n - 1)) promises.foreach(p => g.execute(() => p.tryComplete(Success(()))))
+      p.future
+    })
+  }
+  val tests =
+    Tests(nameTree = Tree("async", testNames: _*), callTree = new TestCallTree(Right(testTrees)))
+}
diff --git a/sbt/src/sbt-test/tests/fork-async/test b/sbt/src/sbt-test/tests/fork-async/test
new file mode 100644
index 000000000..dfffb838b
--- /dev/null
+++ b/sbt/src/sbt-test/tests/fork-async/test
@@ -0,0 +1 @@
+> test
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);