diff --git a/build.sbt b/build.sbt
index 9507d71ac..58c54d7ec 100644
--- a/build.sbt
+++ b/build.sbt
@@ -348,6 +348,10 @@ lazy val stdTaskProj = (project in file("tasks-standard"))
     name := "Task System",
     testExclusive,
     mimaSettings,
+    mimaBinaryIssueFilters ++= Seq(
+      // unused private[sbt]
+      exclude[DirectMissingMethodProblem]("sbt.Task.mapTask"),
+    ),
   )
   .configure(addSbtIO, addSbtUtilLogging, addSbtUtilCache)
 
diff --git a/tasks-standard/src/main/scala/sbt/Action.scala b/tasks-standard/src/main/scala/sbt/Action.scala
index 9489c75e9..914bb6701 100644
--- a/tasks-standard/src/main/scala/sbt/Action.scala
+++ b/tasks-standard/src/main/scala/sbt/Action.scala
@@ -62,7 +62,6 @@ final case class Task[T](info: Info[T], work: Action[T]) {
   override def toString = info.name getOrElse ("Task(" + info + ")")
   override def hashCode = info.hashCode
 
-  private[sbt] def mapTask(g: Task ~> Task): Task[T] = g(Task(info, work.mapTask(g)))
   def tag(tags: Tag*): Task[T] = tagw(tags.map(t => (t, 1)): _*)
   def tagw(tags: (Tag, Int)*): Task[T] =
     copy(info = info.set(tagsKey, info.get(tagsKey).getOrElse(Map.empty) ++ tags))