diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt
index 0e765d6d925..2b3b18ac451 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt
@@ -473,6 +473,9 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
                 value = "null"
                 withGetter = true
             }
+            default("boundSymbol") {
+                isMutable = false
+            }
         }
 
         impl(superReference, "FirExplicitSuperReference")
diff --git a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt
index 11bed1b7dfe..29f4d1fdd4b 100644
--- a/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt
+++ b/compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/model/Field.kt
@@ -93,7 +93,7 @@ class FieldWithDefault(val origin: Field) : Field() {
     }
 }
 
-open class SimpleField(
+class SimpleField(
     override val name: String,
     override val type: String,
     override val packageName: String?,
@@ -105,7 +105,7 @@ open class SimpleField(
     override val fullQualifiedName: String?
         get() = customType?.fullQualifiedName ?: super.fullQualifiedName
 
-    override var isMutable: Boolean = false
+    override var isMutable: Boolean = withReplace
 
     override fun internalCopy(): Field {
         return SimpleField(