diff --git a/main-actions/src/main/scala/sbt/Package.scala b/main-actions/src/main/scala/sbt/Package.scala
index 9970561d4..54d107917 100644
--- a/main-actions/src/main/scala/sbt/Package.scala
+++ b/main-actions/src/main/scala/sbt/Package.scala
@@ -82,7 +82,7 @@ object Package {
 
     val map = conf.sources.toMap
     val inputs = map :+: lastModified(map.keySet) :+: manifest :+: HNil
-    cachedMakeJar(inputs)(exists(conf.jar))
+    cachedMakeJar(inputs)(() => exists(conf.jar))
   }
   def setVersion(main: Attributes): Unit = {
     val version = Attributes.Name.MANIFEST_VERSION