diff --git a/main/src/main/scala/sbt/EvaluateTask.scala b/main/src/main/scala/sbt/EvaluateTask.scala
index 7292ff694..59bf062f3 100644
--- a/main/src/main/scala/sbt/EvaluateTask.scala
+++ b/main/src/main/scala/sbt/EvaluateTask.scala
@@ -480,6 +480,7 @@ object EvaluateTask {
       def cancelAndShutdown(): Unit = {
         println("")
         log.warn("Canceling execution...")
+        ConcurrentRestrictions.cancelAll()
         shutdown()
       }
     }
diff --git a/tasks/src/main/scala/sbt/ConcurrentRestrictions.scala b/tasks/src/main/scala/sbt/ConcurrentRestrictions.scala
index d289c453c..e3ed01c60 100644
--- a/tasks/src/main/scala/sbt/ConcurrentRestrictions.scala
+++ b/tasks/src/main/scala/sbt/ConcurrentRestrictions.scala
@@ -10,6 +10,8 @@ package sbt
 import java.util.concurrent.atomic.AtomicInteger
 
 import sbt.internal.util.AttributeKey
+import java.util.concurrent.atomic.AtomicBoolean
+import java.util.concurrent.RejectedExecutionException
 
 /**
  * Describes restrictions on concurrent execution for a set of tasks.
@@ -48,6 +50,12 @@ import java.util.concurrent.{ Executor, Executors, ExecutorCompletionService }
 import annotation.tailrec
 
 object ConcurrentRestrictions {
+  private[this] val completionServices = new java.util.WeakHashMap[CompletionService[_, _], Boolean]
+  import scala.collection.JavaConverters._
+  def cancelAll() = completionServices.keySet.asScala.toVector.foreach {
+    case a: AutoCloseable => a.close()
+    case _                =>
+  }
 
   /**
    * A ConcurrentRestrictions instance that places no restrictions on concurrently executing tasks.
@@ -138,7 +146,8 @@ object ConcurrentRestrictions {
     val pool = Executors.newCachedThreadPool { r =>
       new Thread(r, s"sbt-completion-service-pool-$id-${i.getAndIncrement()}")
     }
-    (completionService[A, R](pool, tags, warn), () => { pool.shutdownNow(); () })
+    val service = completionService[A, R](pool, tags, warn)
+    (service, () => { service.close(); pool.shutdownNow(); () })
   }
 
   def completionService[A, R](
@@ -147,7 +156,9 @@ object ConcurrentRestrictions {
       isSentinel: A => Boolean
   ): (CompletionService[A, R], () => Unit) = {
     val pool = Executors.newCachedThreadPool()
-    (completionService[A, R](pool, tags, warn, isSentinel), () => {
+    val service = completionService[A, R](pool, tags, warn, isSentinel)
+    (service, () => {
+      service.close()
       pool.shutdownNow()
       ()
     })
@@ -157,7 +168,7 @@ object ConcurrentRestrictions {
       backing: Executor,
       tags: ConcurrentRestrictions[A],
       warn: String => Unit
-  ): CompletionService[A, R] = {
+  ): CompletionService[A, R] with AutoCloseable = {
     completionService[A, R](backing, tags, warn, (_: A) => false)
   }
 
@@ -170,12 +181,18 @@ object ConcurrentRestrictions {
       tags: ConcurrentRestrictions[A],
       warn: String => Unit,
       isSentinel: A => Boolean,
-  ): CompletionService[A, R] = {
+  ): CompletionService[A, R] with AutoCloseable = {
 
     // Represents submitted work for a task.
     final class Enqueue(val node: A, val work: () => R)
 
-    new CompletionService[A, R] {
+    new CompletionService[A, R] with AutoCloseable {
+      completionServices.put(this, true)
+      private[this] val closed = new AtomicBoolean(false)
+      override def close(): Unit = if (closed.compareAndSet(false, true)) {
+        completionServices.remove(this)
+        ()
+      }
 
       /** Backing service used to manage execution on threads once all constraints are satisfied. */
       private[this] val jservice = new ExecutorCompletionService[R](backing)
@@ -190,7 +207,8 @@ object ConcurrentRestrictions {
       private[this] val pending = new LinkedList[Enqueue]
 
       def submit(node: A, work: () => R): Unit = synchronized {
-        if (isSentinel(node)) {
+        if (closed.get) throw new RejectedExecutionException
+        else if (isSentinel(node)) {
           // skip all checks for sentinels
           CompletionService.submit(work, jservice)
         } else {
@@ -253,7 +271,11 @@ object ConcurrentRestrictions {
           submitValid(tried)
         }
 
-      def take(): R = jservice.take().get()
+      def take(): R = {
+        if (closed.get)
+          throw new IllegalStateException("Tried to get values for a closed completion service")
+        jservice.take().get()
+      }
     }
   }
 }