diff --git a/main-command/src/main/scala/sbt/internal/ui/UserThread.scala b/main-command/src/main/scala/sbt/internal/ui/UserThread.scala
index fd6d45778..1e251d1cc 100644
--- a/main-command/src/main/scala/sbt/internal/ui/UserThread.scala
+++ b/main-command/src/main/scala/sbt/internal/ui/UserThread.scala
@@ -13,8 +13,9 @@ import java.util.concurrent.atomic.{ AtomicBoolean, AtomicReference }
 import java.util.concurrent.Executors
 
 import sbt.State
-import sbt.internal.util.{ ConsoleAppender, ProgressEvent, ProgressState, Util }
-import sbt.internal.util.Prompt
+import scala.concurrent.duration._
+import sbt.internal.util.JoinThread._
+import sbt.internal.util.{ ConsoleAppender, ProgressEvent, ProgressState, Prompt }
 
 private[sbt] class UserThread(val channel: CommandChannel) extends AutoCloseable {
   private[this] val uiThread = new AtomicReference[(UITask, Thread)]
@@ -65,14 +66,7 @@ private[sbt] class UserThread(val channel: CommandChannel) extends AutoCloseable
       case null =>
       case (t, thread) =>
         t.close()
-        Util.ignoreResult(thread.interrupt())
-        try thread.join(1000)
-        catch { case _: InterruptedException => }
-
-        // This join should always work, but if it doesn't log an error because
-        // it can cause problems if the thread isn't joined
-        if (thread.isAlive) System.err.println(s"Unable to join thread $thread")
-        ()
+        thread.joinFor(1.second)
     }
   }
   private[sbt] def stopThread(): Unit = uiThread.synchronized(stopThreadImpl())
diff --git a/main-command/src/main/scala/sbt/internal/util/JoinThread.scala b/main-command/src/main/scala/sbt/internal/util/JoinThread.scala
new file mode 100644
index 000000000..e2bee2f07
--- /dev/null
+++ b/main-command/src/main/scala/sbt/internal/util/JoinThread.scala
@@ -0,0 +1,30 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal.util
+
+import scala.annotation.tailrec
+import scala.concurrent.duration._
+
+object JoinThread {
+  implicit class ThreadOps(val t: Thread) extends AnyVal {
+    def joinFor(duration: FiniteDuration): Unit = {
+      val deadline = duration.fromNow
+      var exception: Option[InterruptedException] = None
+      @tailrec def impl(): Unit = {
+        try {
+          t.interrupt()
+          t.join(10)
+        } catch { case e: InterruptedException => exception = Some(e) }
+        if (t.isAlive) impl()
+      }
+      impl()
+      if (t.isAlive) System.err.println(s"Unable to join thread $t after $duration")
+      exception.foreach(throw _)
+    }
+  }
+}
diff --git a/main/src/main/scala/sbt/internal/Continuous.scala b/main/src/main/scala/sbt/internal/Continuous.scala
index be0c1cea1..e7ec8c644 100644
--- a/main/src/main/scala/sbt/internal/Continuous.scala
+++ b/main/src/main/scala/sbt/internal/Continuous.scala
@@ -21,6 +21,7 @@ import sbt.internal.LabeledFunctions._
 import sbt.internal.io.WatchState
 import sbt.internal.nio._
 import sbt.internal.ui.UITask
+import sbt.internal.util.JoinThread._
 import sbt.internal.util.complete.DefaultParsers.{ Space, matched }
 import sbt.internal.util.complete.Parser._
 import sbt.internal.util.complete.{ Parser, Parsers }
@@ -666,15 +667,13 @@ private[sbt] object Continuous extends DeprecatedContinuous {
     }
     def removeThread(thread: Thread): Unit = Util.ignoreResult(threads.remove(thread))
     def close(): Unit = if (closed.compareAndSet(false, true)) {
-      threads.forEach { t =>
-        val deadline = 1.second.fromNow
-        while (t.isAlive && !deadline.isOverdue) {
-          t.interrupt()
-          t.join(10)
-        }
-        if (t.isAlive) System.err.println(s"Couldn't join watch thread $t")
+      var exception: Option[InterruptedException] = None
+      threads.forEach { thread =>
+        try thread.joinFor(1.second)
+        catch { case e: InterruptedException => exception = Some(e) }
       }
       threads.clear()
+      exception.foreach(throw _)
     }
   }
   private object WatchExecutor {
@@ -692,8 +691,8 @@ private[sbt] object Continuous extends DeprecatedContinuous {
         executor: WatchExecutor
     ) extends Future[R] {
       def cancel(): Unit = {
-        thread.interrupt()
         executor.removeThread(thread)
+        thread.joinFor(1.second)
       }
       def result: Try[R] =
         try queue.take match {