diff --git a/visionforge-core/src/commonMain/kotlin/hep/dataforge/vision/VisionGroupBase.kt b/visionforge-core/src/commonMain/kotlin/hep/dataforge/vision/VisionGroupBase.kt
index af8fee4e..fa3567b6 100644
--- a/visionforge-core/src/commonMain/kotlin/hep/dataforge/vision/VisionGroupBase.kt
+++ b/visionforge-core/src/commonMain/kotlin/hep/dataforge/vision/VisionGroupBase.kt
@@ -13,10 +13,12 @@ import kotlinx.serialization.Transient
 @SerialName("vision.group")
 public open class VisionGroupBase : VisionBase(), MutableVisionGroup {
 
-    //protected abstract val _children: MutableMap<NameToken, T>
-
+    /**
+     * Internal mutable container for group children
+     * TODO made protected due to https://github.com/Kotlin/kotlinx.serialization/issues/1200
+     */
     @SerialName("children")
-    protected val childrenInternal = LinkedHashMap<NameToken, Vision>()
+    protected open val childrenInternal: MutableMap<NameToken, Vision> = LinkedHashMap()
 
     /**
      * A map of top level named children
diff --git a/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/SolidGroup.kt b/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/SolidGroup.kt
index d4c76661..d441ab6c 100644
--- a/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/SolidGroup.kt
+++ b/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/SolidGroup.kt
@@ -93,13 +93,17 @@ public fun MutableVisionGroup.group(name: String, action: SolidGroup.() -> Unit
  */
 @Serializable(PrototypesSerializer::class)
 internal class Prototypes(
-    override var children: MutableMap<NameToken, Vision> = LinkedHashMap(),
+    children: Map<NameToken, Vision> = emptyMap(),
 ) : VisionGroupBase(), PrototypeHolder {
 
     override fun styleSheet(block: StyleSheet.() -> Unit) {
         error("Can't define stylesheet for prototypes block")
     }
 
+    init {
+        this.childrenInternal.putAll(children)
+    }
+
     override var properties: Config?
         get() = null
         set(_) {
diff --git a/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/serialization.kt b/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/serialization.kt
index c5b0a435..fafc0c5c 100644
--- a/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/serialization.kt
+++ b/visionforge-solid/src/commonMain/kotlin/hep/dataforge/vision/solid/serialization.kt
@@ -91,7 +91,7 @@ internal object PrototypesSerializer : KSerializer<MutableVisionGroup> {
 
     override fun deserialize(decoder: Decoder): MutableVisionGroup {
         val map = mapSerializer.deserialize(decoder)
-        return Prototypes(map as? MutableMap<NameToken, Vision> ?: LinkedHashMap(map))
+        return Prototypes(map)
     }
 
     override fun serialize(encoder: Encoder, value: MutableVisionGroup) {
diff --git a/visionforge-solid/src/commonTest/kotlin/hep/dataforge/vision/solid/PropertyTest.kt b/visionforge-solid/src/commonTest/kotlin/hep/dataforge/vision/solid/PropertyTest.kt
index a12679e5..02a0b661 100644
--- a/visionforge-solid/src/commonTest/kotlin/hep/dataforge/vision/solid/PropertyTest.kt
+++ b/visionforge-solid/src/commonTest/kotlin/hep/dataforge/vision/solid/PropertyTest.kt
@@ -60,7 +60,7 @@ class PropertyTest {
     @Test
     fun testProxyStyleProperty() {
         var box: Proxy? = null
-        val group = SolidGroup().apply {
+        val group = SolidGroup{
             styleSheet {
                 set("testStyle") {
                     SolidMaterial.MATERIAL_COLOR_KEY put "#555555"