diff --git a/project/Scripted.scala b/project/Scripted.scala
index e77749d63..2b4276a8d 100644
--- a/project/Scripted.scala
+++ b/project/Scripted.scala
@@ -17,8 +17,10 @@ object LocalScriptedPlugin extends AutoPlugin {
 trait ScriptedKeys {
   val publishAll = taskKey[Unit]("")
   val publishLocalBinAll = taskKey[Unit]("")
-  val scriptedUnpublished = inputKey[Unit]("Execute scripted without publishing sbt first. " +
-        "Saves you some time when only your test has changed")
+  val scriptedUnpublished = inputKey[Unit](
+    "Execute scripted without publishing sbt first. " +
+      "Saves you some time when only your test has changed"
+  )
   val scriptedSource = settingKey[File]("")
   val scriptedPrescripted = taskKey[File => Unit]("")
 }
@@ -107,33 +109,48 @@ object Scripted {
     // Interface to cross class loader
     type SbtScriptedRunner = {
       def runInParallel(
-        resourceBaseDirectory: File,
-        bufferLog: Boolean,
-        tests: Array[String],
-        bootProperties: File,
-        launchOpts: Array[String],
-        prescripted: java.util.List[File],
+          resourceBaseDirectory: File,
+          bufferLog: Boolean,
+          tests: Array[String],
+          bootProperties: File,
+          launchOpts: Array[String],
+          prescripted: java.util.List[File],
+          instances: Int
       ): Unit
     }
 
-    val bridge = bridgeClass.getDeclaredConstructor().newInstance().asInstanceOf[SbtScriptedRunner]
-
+    val initLoader = Thread.currentThread.getContextClassLoader
     try {
-      // Using java.util.List to encode File => Unit.
-      val callback = new java.util.AbstractList[File] {
-        override def add(x: File): Boolean = { prescripted(x); false }
-        def get(x: Int): sbt.File = ???
-        def size(): Int = 0
-      }
-      import scala.language.reflectiveCalls
-      bridge.runInParallel(
-        sourcePath,
-        bufferLog,
-        args.toArray,
-        launcher,
-        launchOpts.toArray,
-        callback,
-      )
-    } catch { case ite: InvocationTargetException => throw ite.getCause }
+      Thread.currentThread.setContextClassLoader(loader)
+      val bridge =
+        bridgeClass.getDeclaredConstructor().newInstance().asInstanceOf[SbtScriptedRunner]
+      try {
+        // Using java.util.List to encode File => Unit.
+        val callback = new java.util.AbstractList[File] {
+          override def add(x: File): Boolean = { prescripted(x); false }
+          def get(x: Int): sbt.File = ???
+          def size(): Int = 0
+        }
+        val instances: Int = (System.getProperty("sbt.scripted.parallel.instances") match {
+          case null => 1
+          case i    => scala.util.Try(i.toInt).getOrElse(1)
+        }) match {
+          case i if i > 0 => i
+          case _          => 1
+        }
+        import scala.language.reflectiveCalls
+        bridge.runInParallel(
+          sourcePath,
+          bufferLog,
+          args.toArray,
+          launcher,
+          launchOpts.toArray,
+          callback,
+          instances
+        )
+      } catch { case ite: InvocationTargetException => throw ite.getCause }
+    } finally {
+      Thread.currentThread.setContextClassLoader(initLoader)
+    }
   }
 }
diff --git a/sbt/src/sbt-test/dependency-management/cached-resolution-classifier/test b/sbt/src/sbt-test/dependency-management/cached-resolution-classifier/test
index ccff5f24b..55cfc0713 100644
--- a/sbt/src/sbt-test/dependency-management/cached-resolution-classifier/test
+++ b/sbt/src/sbt-test/dependency-management/cached-resolution-classifier/test
@@ -1,5 +1,3 @@
-> debug
-
 > a/update
 
 > a/updateClassifiers
diff --git a/sbt/src/sbt-test/dependency-management/cached-resolution-conflicts/test b/sbt/src/sbt-test/dependency-management/cached-resolution-conflicts/test
index 8e266c833..1a1446f96 100644
--- a/sbt/src/sbt-test/dependency-management/cached-resolution-conflicts/test
+++ b/sbt/src/sbt-test/dependency-management/cached-resolution-conflicts/test
@@ -1,4 +1,3 @@
 > y1/publishLocal
 > y2/publishLocal
-> debug
 > check
diff --git a/sbt/src/sbt-test/dependency-management/cached-resolution-interproj/test b/sbt/src/sbt-test/dependency-management/cached-resolution-interproj/test
index f3d872ac0..15886c51a 100644
--- a/sbt/src/sbt-test/dependency-management/cached-resolution-interproj/test
+++ b/sbt/src/sbt-test/dependency-management/cached-resolution-interproj/test
@@ -1,4 +1,2 @@
-> debug
-
 > check
 
diff --git a/sbt/src/sbt-test/dependency-management/exclude-transitive/test b/sbt/src/sbt-test/dependency-management/exclude-transitive/test
index bf78e6c17..6204908fb 100644
--- a/sbt/src/sbt-test/dependency-management/exclude-transitive/test
+++ b/sbt/src/sbt-test/dependency-management/exclude-transitive/test
@@ -1,4 +1,3 @@
-> debug
 # load the project definition with transitive dependencies enabled
 # and check that they are not downloaded
 #$ pause
diff --git a/sbt/src/sbt-test/dependency-management/ivy-settings-a/test b/sbt/src/sbt-test/dependency-management/ivy-settings-a/test
index a8347e838..d7b5b2289 100644
--- a/sbt/src/sbt-test/dependency-management/ivy-settings-a/test
+++ b/sbt/src/sbt-test/dependency-management/ivy-settings-a/test
@@ -1,4 +1,3 @@
-> debug
 > update
 # works because scalaVersion is the same as sbtScalaVersion
 > compile
diff --git a/sbt/src/sbt-test/dependency-management/mvn-local/disabled b/sbt/src/sbt-test/dependency-management/mvn-local/disabled
index e6f5381a9..b7eb9f51f 100644
--- a/sbt/src/sbt-test/dependency-management/mvn-local/disabled
+++ b/sbt/src/sbt-test/dependency-management/mvn-local/disabled
@@ -19,7 +19,6 @@ $ copy-file changes/mainB1.scala main/B.scala
 -> main/compile
 
 $ copy-file changes/libA.scala library/A.scala
-> debug
 > library/publishM2
 # should succeed even without 'update' because Ivy should use the jar from the origin and not copy it to its cache
 > main/compile
diff --git a/scripted-sbt-redux/src/main/scala/sbt/scriptedtest/ScriptedTests.scala b/scripted-sbt-redux/src/main/scala/sbt/scriptedtest/ScriptedTests.scala
index 91373e1d0..8375bf835 100644
--- a/scripted-sbt-redux/src/main/scala/sbt/scriptedtest/ScriptedTests.scala
+++ b/scripted-sbt-redux/src/main/scala/sbt/scriptedtest/ScriptedTests.scala
@@ -125,7 +125,10 @@ final class ScriptedTests(
     if (labelsAndDirs.isEmpty) List()
     else {
       val totalSize = labelsAndDirs.size
-      val batchSize = totalSize / sbtInstances
+      val batchSize = totalSize / sbtInstances match {
+        case 0 => 1
+        case s => s
+      }
 
       val (launcherBasedTests, runFromSourceBasedTests) = labelsAndDirs.partition {
         case (testName, _) =>