diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/dukat/AbstractDukatTask.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/dukat/AbstractDukatTask.kt
index 0bd51482bfd..76dfea79480 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/dukat/AbstractDukatTask.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/dukat/AbstractDukatTask.kt
@@ -24,8 +24,8 @@ abstract class AbstractDukatTask(
         get() = true
 
     @get:Internal
-    override val requiredNpmDependencies: Collection<RequiredKotlinJsDependency>
-        get() = listOf(nodeJs.versions.dukat)
+    override val requiredNpmDependencies: Set<RequiredKotlinJsDependency>
+        get() = setOf(nodeJs.versions.dukat)
 
     /**
      * Package name for the generated file (by default filename.d.ts renamed to filename.d.kt)
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsExec.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsExec.kt
index 89c63e16ac0..d03c0480f28 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsExec.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsExec.kt
@@ -44,8 +44,8 @@ constructor(
         get() = true
 
     @get:Internal
-    override val requiredNpmDependencies: Collection<RequiredKotlinJsDependency>
-        get() = mutableListOf<RequiredKotlinJsDependency>().also {
+    override val requiredNpmDependencies: Set<RequiredKotlinJsDependency>
+        get() = mutableSetOf<RequiredKotlinJsDependency>().also {
             if (sourceMapStackTraces) {
                 it.add(nodeJs.versions.sourceMapSupport)
             }
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsRootExtension.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsRootExtension.kt
index 16b271a0c26..949ff97eb65 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsRootExtension.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/nodejs/NodeJsRootExtension.kt
@@ -128,14 +128,14 @@ open class NodeJsRootExtension(val rootProject: Project) : ConfigurationPhaseAwa
 }
 
 class TasksRequirements {
-    val byTask = mutableMapOf<RequiresNpmDependencies, Collection<RequiredKotlinJsDependency>>()
-    val byCompilation = mutableMapOf<KotlinJsCompilation, MutableList<RequiresNpmDependencies>>()
+    val byTask = mutableMapOf<RequiresNpmDependencies, Set<RequiredKotlinJsDependency>>()
+    private val byCompilation = mutableMapOf<KotlinJsCompilation, MutableList<RequiresNpmDependencies>>()
 
     fun getTaskRequirements(compilation: KotlinJsCompilation): Collection<RequiresNpmDependencies> =
         byCompilation[compilation] ?: listOf()
 
     fun addTaskRequirements(task: RequiresNpmDependencies) {
-        val requirements = task.requiredNpmDependencies.toList()
+        val requirements = task.requiredNpmDependencies
 
         byTask[task] = requirements
 
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/npm/RequiresNpmDependencies.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/npm/RequiresNpmDependencies.kt
index 0cf81575e23..ebcf69a9cf0 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/npm/RequiresNpmDependencies.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/npm/RequiresNpmDependencies.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -9,7 +9,8 @@ import org.jetbrains.kotlin.gradle.plugin.mpp.KotlinJsCompilation
 import org.jetbrains.kotlin.gradle.targets.js.RequiredKotlinJsDependency
 
 interface RequiresNpmDependencies {
+
     val compilation: KotlinJsCompilation
     val nodeModulesRequired: Boolean
-    val requiredNpmDependencies: Collection<RequiredKotlinJsDependency>
+    val requiredNpmDependencies: Set<RequiredKotlinJsDependency>
 }
\ No newline at end of file
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/KotlinJsTest.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/KotlinJsTest.kt
index 0505b9f0008..26508264102 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/KotlinJsTest.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/KotlinJsTest.kt
@@ -69,7 +69,7 @@ constructor(
     override val nodeModulesRequired: Boolean
         @Internal get() = testFramework!!.nodeModulesRequired
 
-    override val requiredNpmDependencies: Collection<RequiredKotlinJsDependency>
+    override val requiredNpmDependencies: Set<RequiredKotlinJsDependency>
         @Internal get() = testFramework!!.requiredNpmDependencies
 
     @Deprecated("Use useMocha instead", ReplaceWith("useMocha()"))
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KotlinKarma.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KotlinKarma.kt
index 8aec508a936..333d6c980ca 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KotlinKarma.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/karma/KotlinKarma.kt
@@ -52,8 +52,8 @@ class KotlinKarma(override val compilation: KotlinJsCompilation) :
         project.projectDir.resolve("karma.config.d")
     }
 
-    override val requiredNpmDependencies: Collection<RequiredKotlinJsDependency>
-        get() = requiredDependencies.toList()
+    override val requiredNpmDependencies: Set<RequiredKotlinJsDependency>
+        get() = requiredDependencies
 
     override val settingsState: String
         get() = "KotlinKarma($config)"
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/mocha/KotlinMocha.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/mocha/KotlinMocha.kt
index f84711f8b5b..bd64118cd64 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/mocha/KotlinMocha.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/testing/mocha/KotlinMocha.kt
@@ -30,8 +30,8 @@ class KotlinMocha(override val compilation: KotlinJsCompilation) :
     override val settingsState: String
         get() = "mocha"
 
-    override val requiredNpmDependencies: Collection<RequiredKotlinJsDependency>
-        get() = listOf(
+    override val requiredNpmDependencies: Set<RequiredKotlinJsDependency>
+        get() = setOf(
             versions.kotlinJsTestRunner,
             versions.mocha,
             versions.sourceMapSupport
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpack.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpack.kt
index 36066a75a73..5a9791f598d 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpack.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpack.kt
@@ -198,7 +198,7 @@ constructor(
     override val nodeModulesRequired: Boolean
         @Internal get() = true
 
-    override val requiredNpmDependencies: Collection<RequiredKotlinJsDependency>
+    override val requiredNpmDependencies: Set<RequiredKotlinJsDependency>
         @Internal get() = createRunner().config.getRequiredDependencies(versions)
 
     @TaskAction
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpackConfig.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpackConfig.kt
index 58ccf469b0f..2b19633f756 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpackConfig.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/webpack/KotlinWebpackConfig.kt
@@ -40,7 +40,7 @@ data class KotlinWebpackConfig(
     val resolveFromModulesFirst: Boolean = false
 ) {
     fun getRequiredDependencies(versions: NpmVersions) =
-        mutableListOf<RequiredKotlinJsDependency>().also {
+        mutableSetOf<RequiredKotlinJsDependency>().also {
             it.add(versions.kotlinJsTestRunner)
             it.add(versions.webpack)
             it.add(versions.webpackCli)