diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index f8774dff9..4f83c85f3 100755
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -773,7 +773,7 @@ object Defaults extends BuildCommon {
     class ScalaLoader extends URLClassLoader(allJars.map(_.toURI.toURL).toArray, libraryLoader)
     val fullLoader = classLoaderCache.cachedCustomClassloader(
       allJars.toList,
-      () => new URLClassLoader(allJars.map(_.toURI.toURL).toArray, libraryLoader)
+      () => new ScalaLoader
     )
     new ScalaInstance(
       version,
diff --git a/main/src/main/scala/sbt/internal/ClassLoaders.scala b/main/src/main/scala/sbt/internal/ClassLoaders.scala
index 396d2da31..67963eb80 100644
--- a/main/src/main/scala/sbt/internal/ClassLoaders.scala
+++ b/main/src/main/scala/sbt/internal/ClassLoaders.scala
@@ -230,10 +230,12 @@ private[sbt] object ClassLoaders {
     } else parent
   }
 
+  private[this] class FlatLoader(classpath: Seq[File], parent: ClassLoader)
+      extends URLClassLoader(classpath.map(_.toURI.toURL).toArray, parent) {
+    override def toString: String =
+      s"FlatClassLoader(parent = $interfaceLoader, jars =\n${classpath.mkString("\n")}\n)"
+  }
   // helper methods
   private def flatLoader(classpath: Seq[File], parent: ClassLoader): ClassLoader =
-    new URLClassLoader(classpath.map(_.toURI.toURL).toArray, parent) {
-      override def toString: String =
-        s"FlatClassLoader(parent = $interfaceLoader, jars =\n${classpath.mkString("\n")}\n)"
-    }
+    new FlatLoader(classpath, parent)
 }