diff --git a/library/src-non-bootstrapped/scala/annotation/internal/experimentalTest.scala b/library/src-non-bootstrapped/scala/annotation/internal/experimentalTest.scala
index 1240f9039670..67f672b02c78 100644
--- a/library/src-non-bootstrapped/scala/annotation/internal/experimentalTest.scala
+++ b/library/src-non-bootstrapped/scala/annotation/internal/experimentalTest.scala
@@ -8,3 +8,5 @@ package internal
  *  It may accidentally be visible while compiling the non-bootstrapped library.
  */
 @experimental def testExperimental = 4
+
+// def test = testExperimental // This should fail if un-commented
diff --git a/project/Build.scala b/project/Build.scala
index ecebf6e00fb2..a62c0bc90adf 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -63,7 +63,7 @@ object DottyJSPlugin extends AutoPlugin {
 }
 
 object Build {
-  val referenceVersion = "3.0.0"
+  val referenceVersion = "3.1.0-RC1-bin-20210823-dd7a07a-NIGHTLY"
 
   val baseVersion = "3.1.0-RC1"
 
@@ -1740,7 +1740,10 @@ object Build {
       val base =
         project.withCommonSettings.
           settings(
-            libraryDependencies += "org.scala-lang" % "scala-library" % stdlibVersion
+            libraryDependencies += "org.scala-lang" % "scala-library" % stdlibVersion,
+            // Make sure we do not refer to experimental features outside an experimental scope.
+            // In other words, disable NIGHTLY/SNAPSHOT experimental scope.
+            scalacOptions += "-Yno-experimental",
           ).
           settings(dottyLibrarySettings)
       if (mode == Bootstrapped) {