diff --git a/main/src/main/scala/sbt/internal/server/NetworkChannel.scala b/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
index 828beeab3..5a06c0f8f 100644
--- a/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
+++ b/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
@@ -12,7 +12,13 @@ package server
 import java.io.{ IOException, InputStream, OutputStream }
 import java.net.{ Socket, SocketTimeoutException }
 import java.nio.channels.ClosedChannelException
-import java.util.concurrent.{ ConcurrentHashMap, Executors, LinkedBlockingQueue, TimeUnit }
+import java.util.concurrent.{
+  ConcurrentHashMap,
+  Executors,
+  LinkedBlockingQueue,
+  RejectedExecutionException,
+  TimeUnit
+}
 import java.util.concurrent.atomic.{ AtomicBoolean, AtomicReference }
 
 import sbt.BasicCommandStrings.{ Shutdown, TerminateAction }
@@ -666,25 +672,33 @@ final class NetworkChannel(
       )
     private[this] val buffer = new LinkedBlockingQueue[Byte]
     private[this] val future = new AtomicReference[java.util.concurrent.Future[_]]
-    override def close(): Unit = Util.ignoreResult(executor.shutdownNow())
+    private[this] def doFlush()() = {
+      val list = new java.util.ArrayList[Byte]
+      buffer.synchronized(buffer.drainTo(list))
+      if (!list.isEmpty) jsonRpcNotify(Serialization.systemOut, list.asScala.toSeq)
+    }
+    override def close(): Unit = {
+      Util.ignoreResult(executor.shutdownNow())
+      doFlush()
+    }
     override def write(b: Int): Unit = buffer.synchronized {
       buffer.put(b.toByte)
     }
     override def flush(): Unit = {
       future.get match {
         case null =>
-          future.set(
-            executor.schedule(
-              (() => {
-                future.set(null)
-                val list = new java.util.ArrayList[Byte]
-                buffer.synchronized(buffer.drainTo(list))
-                jsonRpcNotify(Serialization.systemOut, list.asScala.toSeq)
-              }): Runnable,
-              20,
-              TimeUnit.MILLISECONDS
+          try {
+            future.set(
+              executor.schedule(
+                (() => {
+                  future.set(null)
+                  doFlush()
+                }): Runnable,
+                20,
+                TimeUnit.MILLISECONDS
+              )
             )
-          )
+          } catch { case _: RejectedExecutionException => doFlush() }
         case f =>
       }
     }