diff --git a/core/util.runtime/src/org/jetbrains/kotlin/utils/SmartSet.kt b/core/util.runtime/src/org/jetbrains/kotlin/utils/SmartSet.kt
index 64a71eca352..71f8657dd82 100644
--- a/core/util.runtime/src/org/jetbrains/kotlin/utils/SmartSet.kt
+++ b/core/util.runtime/src/org/jetbrains/kotlin/utils/SmartSet.kt
@@ -25,7 +25,7 @@ import java.util.*
  * Also, [iterator] returns an iterator which does not support [MutableIterator.remove].
  */
 @Suppress("UNCHECKED_CAST")
-class SmartSet<T> private constructor() : AbstractSet<T>() {
+class SmartSet<T> private constructor() : AbstractMutableSet<T>() {
     companion object {
         private const val ARRAY_THRESHOLD = 5