diff --git a/joern-cli/frontends/kotlin2cpg/build.sbt b/joern-cli/frontends/kotlin2cpg/build.sbt
index 83032b7c6024..825505cc8cea 100644
--- a/joern-cli/frontends/kotlin2cpg/build.sbt
+++ b/joern-cli/frontends/kotlin2cpg/build.sbt
@@ -23,4 +23,5 @@ libraryDependencies ++= Seq(
 
 enablePlugins(JavaAppPackaging, LauncherJarPlugin)
 trapExit    := false
-Test / fork := false
+Test / fork := true
+Test / javaOptions ++= Seq("-ea")
diff --git a/joern-cli/frontends/kotlin2cpg/src/main/scala/io/joern/kotlin2cpg/types/TypeRenderer.scala b/joern-cli/frontends/kotlin2cpg/src/main/scala/io/joern/kotlin2cpg/types/TypeRenderer.scala
index 1660485f84e8..5b5d79522b43 100644
--- a/joern-cli/frontends/kotlin2cpg/src/main/scala/io/joern/kotlin2cpg/types/TypeRenderer.scala
+++ b/joern-cli/frontends/kotlin2cpg/src/main/scala/io/joern/kotlin2cpg/types/TypeRenderer.scala
@@ -44,6 +44,7 @@ class TypeRenderer(val keepTypeArguments: Boolean = false) {
       case _: ErrorType => cpgUnresolvedType
       case t            => t
     }
+    opts.lock()
     new DescriptorRendererImpl(opts)
   }