diff --git a/platform/collaboration-tools/src/com/intellij/collaboration/util/CollectionDelta.kt b/platform/collaboration-tools/src/com/intellij/collaboration/util/CollectionDelta.kt
index 99f7c22e266c..b4a60abb3c13 100644
--- a/platform/collaboration-tools/src/com/intellij/collaboration/util/CollectionDelta.kt
+++ b/platform/collaboration-tools/src/com/intellij/collaboration/util/CollectionDelta.kt
@@ -2,8 +2,10 @@
 package com.intellij.collaboration.util
 
 class CollectionDelta<out T>(oldCollection: Collection<T>, val newCollection: Collection<T>) {
-  val newItems: Collection<T> = newCollection - oldCollection.toSet()
-  val removedItems: Collection<T> = oldCollection - newCollection.toSet()
+  val newItems: Collection<T> = newCollection - oldCollection.asSet()
+  val removedItems: Collection<T> = oldCollection - newCollection.asSet()
+
+  private fun <T> Collection<T>.asSet() = ((this as? Set<T>) ?: toSet())
 
   val isEmpty = newItems.isEmpty() && removedItems.isEmpty()
 }
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