diff --git a/compiler/test/dotty/tools/vulpix/TestConfiguration.scala b/compiler/test/dotty/tools/vulpix/TestConfiguration.scala
index 23b4479f9fd4..b02b8f6737d2 100644
--- a/compiler/test/dotty/tools/vulpix/TestConfiguration.scala
+++ b/compiler/test/dotty/tools/vulpix/TestConfiguration.scala
@@ -17,6 +17,7 @@ object TestConfiguration {
   )
 
   val classPath = mkClassPath(Jars.dottyTestDeps)
+  val runClassPath = mkClassPath(Jars.dottyLib :: Nil)
 
   def mkClassPath(classPaths: List[String]): String = {
     classPaths map { p =>
@@ -46,7 +47,7 @@ object TestConfiguration {
   val yCheckOptions = Array("-Ycheck:tailrec,resolveSuper,erasure,mixin,getClass,elimStaticThis,labelDef")
 
   val basicDefaultOptions = checkOptions ++ noCheckOptions ++ yCheckOptions
-  val defaultUnoptimised = TestFlags(classPath, basicDefaultOptions)
+  val defaultUnoptimised = TestFlags(classPath, runClassPath, basicDefaultOptions)
   val defaultOptimised = defaultUnoptimised and "-optimise"
   val defaultOptions = defaultUnoptimised
   val allowDeepSubtypes = defaultOptions without "-Yno-deep-subtypes"
diff --git a/compiler/test/dotty/tools/vulpix/TestFlags.scala b/compiler/test/dotty/tools/vulpix/TestFlags.scala
index 221da457f9b4..5dbfc12f11d9 100644
--- a/compiler/test/dotty/tools/vulpix/TestFlags.scala
+++ b/compiler/test/dotty/tools/vulpix/TestFlags.scala
@@ -14,6 +14,9 @@ final case class TestFlags(
   def withClasspath(classPath: String): TestFlags =
     TestFlags(s"$defaultClassPath:$classPath", runClassPath, options)
 
+  def withRunClasspath(classPath: String): TestFlags =
+    TestFlags(defaultClassPath, s"$runClassPath:$classPath", options)
+
   def all: Array[String] = Array("-classpath", defaultClassPath) ++ options
 }