diff --git a/COMPILING.md b/COMPILING.md
index 40f2b96c..68c2ea1e 100644
--- a/COMPILING.md
+++ b/COMPILING.md
@@ -50,7 +50,10 @@ Test suite is useful if you plan on modifying the compiler. Some test dependenci
 
 #### Prerequisites
 
-* JDK 1.8 with Nashorn (tests don't work on newer versions)
+* JDK 1.8 or later
+
+    * Millfork up to version 0.3.22 used to require exactly JDK 1.8 with Nashorn, 
+    as the tests didn't work on newer versions
 
 * sbt
 
diff --git a/build.sbt b/build.sbt
index 6fb93b1d..891447eb 100644
--- a/build.sbt
+++ b/build.sbt
@@ -32,6 +32,12 @@ libraryDependencies += "eu.rekawek.coffeegb" % "coffee-gb" % "1.0.0" % "test"
 
 libraryDependencies += "roug.org.osnine" % "osnine-core" % "2.0-SNAPSHOT" % "test"
 
+libraryDependencies += "org.graalvm.sdk" % "graal-sdk" % "20.2.0" % "test"
+
+libraryDependencies += "org.graalvm.js" % "js" % "20.2.0" % "test"
+
+libraryDependencies += "org.graalvm.js" % "js-scriptengine" % "20.2.0" % "test"
+
 mainClass in Compile := Some("millfork.Main")
 
 assemblyJarName := "millfork.jar"
diff --git a/src/test/scala/millfork/test/emu/NashornEmulator.scala b/src/test/scala/millfork/test/emu/NashornEmulator.scala
index 86e4ab0e..659f83c0 100644
--- a/src/test/scala/millfork/test/emu/NashornEmulator.scala
+++ b/src/test/scala/millfork/test/emu/NashornEmulator.scala
@@ -1,27 +1,27 @@
 package millfork.test.emu
 
-import javax.script.{Bindings, ScriptEngine, ScriptEngineManager}
-import java.io.FileReader
-import java.nio.file.Paths
+import java.nio.file.{Files, Paths}
 
-import jdk.nashorn.api.scripting.ScriptObjectMirror
+import org.graalvm.polyglot.{Context, Value}
 
 import scala.language.dynamics
 
 /**
+  * Despite its name, it no longer uses Nashorn, but GraalJS instead.
   * @author Karol Stasiak
   */
 object NashornEmulator {
 
-  lazy val engine: ScriptEngine = {
-    val jsFile = Paths.get(classOf[Nothing].getResource("/cpu.js").toURI).toFile
-    val engine: ScriptEngine = new ScriptEngineManager().getEngineByName("nashorn")
-    engine.eval(new FileReader(jsFile))
-    engine
+  lazy val engine: Context = {
+    val jsFile = Paths.get(classOf[Nothing].getResource("/cpu.js").toURI)
+    import org.graalvm.polyglot.Context
+    val polyglot = Context.create()
+    polyglot.eval("js", new String(Files.readAllBytes(jsFile)))
+    polyglot
   }
 
   private def newCpu(): JsObject = {
-    JsObject(engine.get("CPU_65816").asInstanceOf[ScriptObjectMirror]).construct()
+    JsObject(engine.eval("js", "CPU_65816")).construct()
   }
 
   def run(memory: Array[Byte], steps: Long, start: Int): (Long, Array[Byte]) = {
@@ -32,14 +32,15 @@ object NashornEmulator {
     val memory0 = cpu.mmu.memory.!("0")
     for (i <- 0 until 1 << 16) memory0.!(i.toString, memory(i) & 0xff)
     cpu.r.pc = start
+    cpu.r.sp = 0x1ff
     cpu.r.k = 0
     var count = 0L
-    while (count < steps && cpu.r.s.*[Number].intValue().&(0xff) > 1) {
+    while (count < steps && cpu.r.s.toInt.&(0xff) > 1) {
       cpu.step()
       count += 1
     }
-    val newMemory = (0 until 1 << 16).map(i => memory0.!(i.toString).*[Number].byteValue()).toArray
-    val cycles = cpu.cycle_count.*[Number].longValue()
+    val newMemory = (0 until 1 << 16).map(i => memory0.!(i.toString).toByte).toArray
+    val cycles = cpu.cycle_count.toLong
     cycles -> newMemory
   }
 
@@ -52,60 +53,74 @@ object NashornEmulator {
   }
 }
 
-case class JsObject(private val mirror: Any) extends Dynamic {
+case class JsObject(private val mirror: Value) extends Dynamic {
 
+  def !(index: Long): JsObject = {
+    if (mirror.hasArrayElements) return JsObject(mirror.getArrayElement(index))
+    else throw new IllegalArgumentException(s"Accessing index $index of $getUnderlyingClass")
+  }
 
-  def !(index: JsObject): JsObject =
-    mirror match {
-      case x: ScriptObjectMirror => JsObject(x.get(index.mirror))
-      case _ => throw new IllegalArgumentException(s"Accessing field $index of $getUnderlyingClass")
-    }
+  def !(index: String): JsObject = {
+    if (mirror.hasMembers) return JsObject(mirror.getMember(index))
+    else throw new IllegalArgumentException(s"Accessing field $index of $getUnderlyingClass")
+  }
 
-  def !(index: Any): JsObject =
-    mirror match {
-      case x: ScriptObjectMirror => JsObject(x.get(index))
-      case _ => throw new IllegalArgumentException(s"Accessing field $index of $getUnderlyingClass")
-    }
+  def !(index: String, value: JsObject): Unit = {
+    if (mirror.hasMembers) mirror.putMember(index, value.mirror)
+    else throw new IllegalArgumentException(s"Setting field $index of $getUnderlyingClass")
+  }
 
-  def !(index: String, value:Any): Unit =
-    mirror match {
-      case x: ScriptObjectMirror => x.setMember(index, value)
-      case _ => throw new IllegalArgumentException(s"Setting field $index of $getUnderlyingClass")
-    }
+  def !(index: String, value:Any): Unit = {
+    if (mirror.hasMembers) mirror.putMember(index, value)
+    else throw new IllegalArgumentException(s"Setting field $index of $getUnderlyingClass")
+  }
 
-  def selectDynamic(name: String): JsObject =
-    mirror match {
-      case x: ScriptObjectMirror => JsObject(x.get(name).asInstanceOf[Any] match {
-        case y: Double => if (y.isValidInt) y.toInt else y
-        case y => y
-      })
-      case _ => throw new IllegalArgumentException(s"Accessing field $name of $getUnderlyingClass")
-    }
+  def !(index: Long, value: JsObject): Unit = {
+    if (mirror.hasArrayElements) mirror.setArrayElement(index, value.mirror)
+    else throw new IllegalArgumentException(s"Setting field $index of $getUnderlyingClass")
+  }
+
+  def !(index: Long, value:Any): Unit = {
+    if (mirror.hasArrayElements) mirror.setArrayElement(index, value)
+    else throw new IllegalArgumentException(s"Setting field $index of $getUnderlyingClass")
+  }
+
+  def selectDynamic(name: String): JsObject = {
+    if (mirror.hasMembers) return JsObject(mirror.getMember(name))
+    else throw new IllegalArgumentException(s"Accessing field $name of $getUnderlyingClass")
+  }
 
   private def getUnderlyingClass = {
     if (mirror.asInstanceOf[AnyRef] eq null) "null" else mirror.getClass.getSimpleName
   }
 
-  def updateDynamic(name: String)(value: Any): Unit =
-    mirror match {
-      case x: ScriptObjectMirror => x.setMember(name, value)
-      case _ => throw new IllegalArgumentException(s"Setting field $name of $getUnderlyingClass")
+  def updateDynamic(name: String)(value: Any): Unit = {
+    if (mirror.hasMembers) {
+      value match {
+        case o:JsObject =>
+          mirror.putMember(name, o.mirror)
+        case _ =>
+          mirror.putMember(name, value)
+      }
     }
+    else throw new IllegalArgumentException(s"Setting field $name of $getUnderlyingClass")
+  }
 
-  def applyDynamic(name: String)(params: Any*): JsObject =
-    mirror match {
-      case x: ScriptObjectMirror => JsObject(x.callMember(name, params.toArray))
-      case _ => throw new IllegalArgumentException(s"Accessing field $name of $getUnderlyingClass")
-    }
+  def applyDynamic(name: String)(params: Any*): JsObject = {
+    if (mirror.canInvokeMember(name)) JsObject(mirror.invokeMember(name, params.toArray))
+    else throw new IllegalArgumentException(s"Invoking method $name of $getUnderlyingClass")
+  }
 
-  def construct(params: Any*): JsObject =
-    mirror match {
-      case x: ScriptObjectMirror => JsObject(x.newObject(params.toArray))
-      case _ => throw new IllegalArgumentException(s"Using $getUnderlyingClass as a constructor")
-    }
+  def construct(params: Any*): JsObject = {
+    if (mirror.canInstantiate) JsObject(mirror.newInstance(params.toArray))
+    else throw new IllegalArgumentException(s"Using $getUnderlyingClass as a constructor")
+  }
 
-  @inline
-  def *[T]: T = mirror.asInstanceOf[T]
+  def toInt: Int = mirror.asInt()
+
+  def toLong: Long = mirror.asLong()
+
+  def toByte: Byte = mirror.asInt().toByte
 
   override def toString: String = String.valueOf(mirror)
 }