diff --git a/js/js.libraries/src/core/javautilCode.kt b/js/js.libraries/src/core/javautilCode.kt
index aca1078f143..3e4a935a5b6 100644
--- a/js/js.libraries/src/core/javautilCode.kt
+++ b/js/js.libraries/src/core/javautilCode.kt
@@ -36,7 +36,7 @@ public object Collections {
     }
 
     library
-    public fun <T> reverse(list: List<T>): Unit {
+    public fun <T> reverse(list: MutableList<T>): Unit {
         val size = list.size()
         for (i in 0.rangeTo(size / 2)) {
             val i2 = size - i
diff --git a/js/js.libraries/src/core/string.kt b/js/js.libraries/src/core/string.kt
index e96ed924991..6e803d81eca 100644
--- a/js/js.libraries/src/core/string.kt
+++ b/js/js.libraries/src/core/string.kt
@@ -1,7 +1,5 @@
 package js
 
-import java.util.List
-
 native public fun String.toUpperCase() : String = js.noImpl
 
 native public fun String.toLowerCase() : String = js.noImpl
diff --git a/js/js.libraries/src/stdlib/JUMapsCode.kt b/js/js.libraries/src/stdlib/JUMapsCode.kt
index 5cb0940e21c..e7dc84675fe 100644
--- a/js/js.libraries/src/stdlib/JUMapsCode.kt
+++ b/js/js.libraries/src/stdlib/JUMapsCode.kt
@@ -1,10 +1,9 @@
 package kotlin
 
-import java.util.Map
 import java.util.HashMap
 
 /** Provides [] access to maps */
-public fun <K, V> Map<K, V>.set(key : K, value : V): Unit {
+public fun <K, V> MutableMap<K, V>.set(key : K, value : V): Unit {
     this.put(key, value)
 }
 
diff --git a/js/js.libraries/src/stdlib/jutilCode.kt b/js/js.libraries/src/stdlib/jutilCode.kt
index a62e5f17834..0b35aa32888 100644
--- a/js/js.libraries/src/stdlib/jutilCode.kt
+++ b/js/js.libraries/src/stdlib/jutilCode.kt
@@ -6,7 +6,7 @@ public inline fun <T> Iterable<T>.toString(): String {
     return makeString(", ", "[", "]")
 }
 
-public inline fun <T> java.util.List<T>.equals(that: List<T>): Boolean {
+public inline fun <T> List<T>.equals(that: List<T>): Boolean {
     val s1 = this.size()
     val s2 = that.size()
     if (s1 == s2) {
@@ -45,7 +45,7 @@ public inline fun hashSet<T>(vararg values: T) : HashSet<T> {
  *
  * @includeFunctionBody ../../test/CollectionTest.kt map
  */
-public inline fun <K,V,R> java.util.Map<K,V>.map(transform: (java.util.Map.Entry<K,V>) -> R) : java.util.List<R> {
+public inline fun <K,V,R> Map<K,V>.map(transform: (Map.Entry<K,V>) -> R) : List<R> {
     return mapTo(java.util.ArrayList<R>(), transform)
 }
 
@@ -55,8 +55,8 @@ public inline fun <K,V,R> java.util.Map<K,V>.map(transform: (java.util.Map.Entry
  *
  * @includeFunctionBody ../../test/MapTest.kt mapValues
  */
-public inline fun <K,V,R> java.util.Map<K,V>.mapValues(transform : (java.util.Map.Entry<K,V>) -> R): java.util.Map<K,R> {
-    return mapValuesTo(java.util.HashMap<K,R>(), transform)
+public inline fun <K,V,R> MutableMap<K,V>.mapValues(transform : (Map.Entry<K,V>) -> R): Map<K,R> {
+    return mapValuesTo(HashMap<K,R>(), transform)
 }
 
 
@@ -65,6 +65,6 @@ public inline fun <K,V,R> java.util.Map<K,V>.mapValues(transform : (java.util.Ma
  *
  * @includeFunctionBody ../../test/CollectionTest.kt map
  */
-public inline fun <T, R> java.util.Collection<T>.map(transform : (T) -> R) : java.util.List<R> {
+public inline fun <T, R> Collection<T>.map(transform : (T) -> R) : List<R> {
     return mapTo(java.util.ArrayList<R>(), transform)
 }
diff --git a/js/js.translator/testFiles/expression/misc/cases/iterableExtension.kt b/js/js.translator/testFiles/expression/misc/cases/iterableExtension.kt
index 24e7c12027e..eabf122231e 100644
--- a/js/js.translator/testFiles/expression/misc/cases/iterableExtension.kt
+++ b/js/js.translator/testFiles/expression/misc/cases/iterableExtension.kt
@@ -3,7 +3,7 @@ package foo
 import java.util.*
 import java.lang.*
 
-public inline fun <T, C: Collection<in T>> Iterator<T>.takeWhileTo(result: C, predicate: (T) -> Boolean) : C {
+public inline fun <T, C: MutableCollection<in T>> Iterator<T>.takeWhileTo(result: C, predicate: (T) -> Boolean) : C {
     for (element in this) if (predicate(element)) result.add(element) else break
     return result
 }
diff --git a/js/js.translator/testFiles/webDemoCanvasExamples/cases/Creatures.kt b/js/js.translator/testFiles/webDemoCanvasExamples/cases/Creatures.kt
index 3ee7c64d49d..c91e2484624 100644
--- a/js/js.translator/testFiles/webDemoCanvasExamples/cases/Creatures.kt
+++ b/js/js.translator/testFiles/webDemoCanvasExamples/cases/Creatures.kt
@@ -9,7 +9,6 @@ import js.jquery.*
 import js.dom.html5.CanvasGradient
 import js.dom.html5.HTMLCanvasElement
 import java.util.ArrayList
-import java.util.List
 import js.dom.html.window
 import js.dom.html.HTMLElement
 import js.dom.html.HTMLImageElement
diff --git a/js/js.translator/testFiles/webDemoExamples2/cases/life.kt b/js/js.translator/testFiles/webDemoExamples2/cases/life.kt
index ac398d54a55..a525dc79193 100644
--- a/js/js.translator/testFiles/webDemoExamples2/cases/life.kt
+++ b/js/js.translator/testFiles/webDemoExamples2/cases/life.kt
@@ -126,7 +126,7 @@ fun <T> Array<T>.toList() : List<T> = this.to(ArrayList<T>())
 val String?.size : Int
 get() = if (this != null) this.length else 0;
 
-fun <T, C: Collection<T>> Array<T>.to(result: C) : C {
+fun <T, C: MutableCollection<T>> Array<T>.to(result: C) : C {
     for (elem in this)
         result.add(elem)
     return result
@@ -162,6 +162,6 @@ fun makeField(s : String) : Field {
 // An excerpt from the Standard Library
 val String?.indices : IntRange get() = IntRange(0, this.sure().size)
 
-fun <K, V> Map<K, V>.set(k : K, v : V) { put(k, v) }
+fun <K, V> MutableMap<K, V>.set(k : K, v : V) { put(k, v) }
 
 val <T> Array<T>.isEmpty : Boolean get() = size == 0