diff --git a/build.gradle.kts b/build.gradle.kts
index fb4aa094..1fc099d2 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -2,7 +2,7 @@ import org.gradle.api.tasks.testing.logging.TestExceptionFormat
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
 plugins {
-    kotlin("jvm") version "1.9.23" // can't v-bump until this is fixed: https://youtrack.jetbrains.com/issue/KT-68361/Function0-not-serializable
+    kotlin("jvm") version "2.0.0"
     `maven-publish`
     signing
 }
diff --git a/karibu-testing-v10/kt10-tests/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadinTest.kt b/karibu-testing-v10/kt10-tests/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadinTest.kt
index 69d991f7..cde521f9 100644
--- a/karibu-testing-v10/kt10-tests/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadinTest.kt
+++ b/karibu-testing-v10/kt10-tests/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadinTest.kt
@@ -83,6 +83,7 @@ internal fun DynaNodeGroup.mockVaadinTest() {
         }
 
         test("serializable") {
+            System.setProperty("sun.io.serialization.extendedDebugInfo", "true") // https://mvysny.github.io/NotSerializableException/
             UI.getCurrent().cloneBySerialization()
             VaadinSession.getCurrent().cloneBySerialization()
             // even that it says it's Serializable it's really not.
diff --git a/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadin.kt b/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadin.kt
index 50627378..15cc249b 100644
--- a/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadin.kt
+++ b/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/MockVaadin.kt
@@ -63,9 +63,9 @@ public object MockVaadin {
     @JvmStatic
     @JvmOverloads
     public fun setup(routes: Routes = Routes(),
-              uiFactory: () -> UI = { MockedUI() }) {
+              uiFactory: () -> UI = @JvmSerializableLambda { MockedUI() }) {
         // init servlet
-        val servlet = MockVaadinServlet(routes)
+        val servlet = MockVaadinServlet(routes, uiFactory)
         setup(uiFactory, servlet)
     }
 
@@ -86,7 +86,7 @@ public object MockVaadin {
      * on what methods you must override in your custom service.
      */
     @JvmStatic
-    public fun setup(uiFactory: () -> UI = { MockedUI() }, servlet: VaadinServlet) {
+    public fun setup(uiFactory: () -> UI = @JvmSerializableLambda { MockedUI() }, servlet: VaadinServlet) {
         check(VaadinVersion.get.isAtLeast(24)) {
             "Karibu-Testing 2.x only works with Vaadin 24+ but you're using ${VaadinVersion.get}"
         }
diff --git a/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockService.kt b/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockService.kt
index 133ef46b..03250f2e 100644
--- a/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockService.kt
+++ b/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockService.kt
@@ -19,7 +19,7 @@ import com.vaadin.flow.server.VaadinSession
  */
 public open class MockService(servlet: VaadinServlet,
                               deploymentConfiguration: DeploymentConfiguration,
-                              public val uiFactory: () -> UI = { MockedUI() }
+                              public val uiFactory: () -> UI = @JvmSerializableLambda { MockedUI() }
 ) : VaadinServletService(servlet, deploymentConfiguration) {
     // need to have this override. Setting `VaadinService.atmosphereAvailable` to false via
     // reflection after the servlet has been initialized is too late, since Atmo is initialized
diff --git a/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockVaadinServlet.kt b/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockVaadinServlet.kt
index 9ee14ac0..d69aa1e7 100644
--- a/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockVaadinServlet.kt
+++ b/karibu-testing-v10/src/main/kotlin/com/github/mvysny/kaributesting/v10/mock/MockVaadinServlet.kt
@@ -18,7 +18,7 @@ import java.lang.reflect.Method
  */
 public open class MockVaadinServlet @JvmOverloads constructor(
         public val routes: Routes = Routes(),
-        public val uiFactory: () -> UI = { MockedUI() }
+        public val uiFactory: () -> UI = @JvmSerializableLambda { MockedUI() }
 ) : VaadinServlet() {
 
     @Throws(ServletException::class)