diff --git a/main/Defaults.scala b/main/Defaults.scala
index 30a00dd88..e1c84b169 100644
--- a/main/Defaults.scala
+++ b/main/Defaults.scala
@@ -60,7 +60,8 @@ object Defaults extends BuildCommon
 		cancelable :== false,
 		autoScalaLibrary :== true,
 		onLoad <<= onLoad ?? idFun[State],
-		onUnload <<= onUnload ?? idFun[State],
+		onUnload <<= (onUnload ?? idFun[State]),
+		onUnload <<= (onUnload, taskTemporaryDirectory) { (f, dir) => s => { try f(s) finally IO.delete(dir) } },
 		watchingMessage <<= watchingMessage ?? Watched.defaultWatchingMessage,
 		triggeredMessage <<= triggeredMessage ?? Watched.defaultTriggeredMessage,
 		definesClass :== FileValueCache(Locate.definesClass _ ).get,