diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index 56706d639..bcefc8b4e 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -4,7 +4,7 @@ import sbt.contraband.ContrabandPlugin.autoImport._
 
 object Dependencies {
   // WARNING: Please Scala update versions in PluginCross.scala too
-  val scala212 = "2.12.4"
+  val scala212 = "2.12.5"
   val baseScalaVersion = scala212
 
   // sbt modules
diff --git a/tasks/src/main/scala/sbt/CompletionService.scala b/tasks/src/main/scala/sbt/CompletionService.scala
index f6fc3a957..88f00a5e8 100644
--- a/tasks/src/main/scala/sbt/CompletionService.scala
+++ b/tasks/src/main/scala/sbt/CompletionService.scala
@@ -17,7 +17,8 @@ import java.util.concurrent.{
   CompletionService => JCompletionService,
   Executor,
   Executors,
-  ExecutorCompletionService
+  ExecutorCompletionService,
+  RejectedExecutionException,
 }
 
 object CompletionService {
@@ -33,7 +34,9 @@ object CompletionService {
       def take() = completion.take().get()
     }
   def submit[T](work: () => T, completion: JCompletionService[T]): () => T = {
-    val future = completion.submit { new Callable[T] { def call = work() } }
+    val future = try completion.submit { new Callable[T] { def call = work() } } catch {
+      case _: RejectedExecutionException => throw Incomplete(None, message = Some("cancelled"))
+    }
     () =>
       future.get()
   }
diff --git a/tasks/src/main/scala/sbt/Execute.scala b/tasks/src/main/scala/sbt/Execute.scala
index 267a1383a..c5d16288e 100644
--- a/tasks/src/main/scala/sbt/Execute.scala
+++ b/tasks/src/main/scala/sbt/Execute.scala
@@ -8,7 +8,7 @@
 package sbt
 
 import sbt.internal.util.ErrorHandling.wideConvert
-import sbt.internal.util.{ DelegatingPMap, PMap, RMap, IDSet, ~> }
+import sbt.internal.util.{ DelegatingPMap, IDSet, PMap, RMap, ~> }
 import sbt.internal.util.Types._
 import Execute._
 
@@ -77,6 +77,7 @@ private[sbt] final class Execute[A[_] <: AnyRef](
 
   def run[T](root: A[T])(implicit strategy: Strategy): Result[T] =
     try { runKeep(root)(strategy)(root) } catch { case i: Incomplete => Inc(i) }
+
   def runKeep[T](root: A[T])(implicit strategy: Strategy): RMap[A, Result] = {
     assert(state.isEmpty, "Execute already running/ran.")