diff --git a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt
index a7c2ef03a2d..4a39aa36bc2 100644
--- a/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt
+++ b/js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/removeUnusedFunctionDefinitions.kt
@@ -34,7 +34,7 @@ fun removeUnusedFunctionDefinitions(root: JsNode, functions: Map<JsName, JsFunct
     val removable = with(UnusedLocalFunctionsCollector(functions)) {
         process()
         accept(root)
-        removableFunctions
+        removableFunctions.toSet()
     }
 
     NodeRemover(JsStatement::class.java) { statement ->