diff --git a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/BaseTransformedType.kt b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/BaseTransformedType.kt
index b4d7cb7ca8d..81de13ceef5 100644
--- a/compiler/fir/tree/src/org/jetbrains/kotlin/fir/BaseTransformedType.kt
+++ b/compiler/fir/tree/src/org/jetbrains/kotlin/fir/BaseTransformedType.kt
@@ -5,4 +5,7 @@
 
 package org.jetbrains.kotlin.fir
 
+// This annotation marks FIR interfaces which may be used as transformer function results
+// In case some interface is not marked, transformer function returns closest parent marked with this annotation
+
 annotation class BaseTransformedType
\ No newline at end of file