diff --git a/compiler/frontend/src/jet/Collections.jet b/compiler/frontend/src/jet/Collections.jet
index 866cd5e533f..c7bbbaf1c19 100644
--- a/compiler/frontend/src/jet/Collections.jet
+++ b/compiler/frontend/src/jet/Collections.jet
@@ -71,6 +71,13 @@ public trait MutableList<E> : List<E>, MutableCollection<E> {
     public fun set(index : Int, element : E) : E
     public fun add(index : Int, element : E)
     public fun remove(index : Int) : E
+
+    // List Iterators
+    override fun listIterator() : MutableListIterator<E>
+    override fun listIterator(index : Int) : MutableListIterator<E>
+
+    // View
+    override fun subList(fromIndex : Int, toIndex : Int) : MutableList<E>
 }
 
 public trait Set<out E> : Collection<E> {
@@ -130,7 +137,9 @@ public trait MutableMap<K, V> : Map<K, V> {
     public fun clear()
 
     // Views
-    override fun entrySet() : Set<MutableMap.MutableEntry<K, V>>
+    override fun keySet() : MutableSet<K>
+    override fun values() : MutableCollection<V>
+    override fun entrySet() : MutableSet<MutableMap.MutableEntry<K, V>>
 
     public trait MutableEntry<K,V> : Map.Entry<K, V>, Hashable {
 	public fun setValue(value : V) : V
diff --git a/compiler/testData/builtin-classes.txt b/compiler/testData/builtin-classes.txt
index b42cfa02fc4..f4994d4f308 100644
--- a/compiler/testData/builtin-classes.txt
+++ b/compiler/testData/builtin-classes.txt
@@ -920,15 +920,15 @@ public abstract trait jet.MutableList</*0*/ E : jet.Any?> : jet.List<E>, jet.Mut
     public abstract override /*2*/ /*fake_override*/ fun isEmpty(): jet.Boolean
     public abstract override /*2*/ /*fake_override*/ fun iterator(): jet.Iterator<E>
     public abstract override /*1*/ /*fake_override*/ fun lastIndexOf(/*0*/ o: jet.Any?): jet.Int
-    public abstract override /*1*/ /*fake_override*/ fun listIterator(): jet.ListIterator<E>
-    public abstract override /*1*/ /*fake_override*/ fun listIterator(/*0*/ index: jet.Int): jet.ListIterator<E>
+    public abstract override /*1*/ fun listIterator(): jet.MutableListIterator<E>
+    public abstract override /*1*/ fun listIterator(/*0*/ index: jet.Int): jet.MutableListIterator<E>
     public abstract fun remove(/*0*/ index: jet.Int): E
     public abstract override /*1*/ fun remove(/*0*/ o: jet.Any?): jet.Boolean
     public abstract override /*1*/ fun removeAll(/*0*/ c: jet.Collection<out jet.Any?>): jet.Boolean
     public abstract override /*1*/ fun retainAll(/*0*/ c: jet.Collection<out jet.Any?>): jet.Boolean
     public abstract fun set(/*0*/ index: jet.Int, /*1*/ element: E): E
     public abstract override /*2*/ /*fake_override*/ fun size(): jet.Int
-    public abstract override /*1*/ /*fake_override*/ fun subList(/*0*/ fromIndex: jet.Int, /*1*/ toIndex: jet.Int): jet.List<E>
+    public abstract override /*1*/ fun subList(/*0*/ fromIndex: jet.Int, /*1*/ toIndex: jet.Int): jet.MutableList<E>
     public abstract override /*2*/ /*fake_override*/ fun toArray(): jet.Array<jet.Any?>
     public abstract override /*2*/ /*fake_override*/ fun </*0*/ T : jet.Any?>toArray(/*0*/ a: jet.Array<out T>): jet.Array<T>
 }
@@ -947,7 +947,7 @@ public abstract trait jet.MutableMap</*0*/ K : jet.Any?, /*1*/ V : jet.Any?> : j
     public abstract fun clear(): jet.Tuple0
     public abstract override /*1*/ /*fake_override*/ fun containsKey(/*0*/ key: jet.Any?): jet.Boolean
     public abstract override /*1*/ /*fake_override*/ fun containsValue(/*0*/ value: jet.Any?): jet.Boolean
-    public abstract override /*1*/ fun entrySet(): jet.Set<jet.MutableMap.MutableEntry<K, V>>
+    public abstract override /*1*/ fun entrySet(): jet.MutableSet<jet.MutableMap.MutableEntry<K, V>>
     public abstract override /*1*/ /*fake_override*/ fun get(/*0*/ key: jet.Any?): V?
     public abstract override /*1*/ /*fake_override*/ fun isEmpty(): jet.Boolean
     public abstract trait jet.MutableMap.MutableEntry</*0*/ K : jet.Any?, /*1*/ V : jet.Any?> : jet.Map.Entry<K, V>, jet.Hashable {
@@ -957,12 +957,12 @@ public abstract trait jet.MutableMap</*0*/ K : jet.Any?, /*1*/ V : jet.Any?> : j
         public abstract override /*2*/ /*fake_override*/ fun hashCode(): jet.Int
         public abstract fun setValue(/*0*/ value: V): V
     }
-    public abstract override /*1*/ /*fake_override*/ fun keySet(): jet.Set<K>
+    public abstract override /*1*/ fun keySet(): jet.MutableSet<K>
     public abstract fun put(/*0*/ key: K, /*1*/ value: V): V?
     public abstract fun putAll(/*0*/ m: jet.Map<out K, out V>): jet.Tuple0
     public abstract fun remove(/*0*/ key: jet.Any?): V?
     public abstract override /*1*/ /*fake_override*/ fun size(): jet.Int
-    public abstract override /*1*/ /*fake_override*/ fun values(): jet.Collection<V>
+    public abstract override /*1*/ fun values(): jet.MutableCollection<V>
 }
 public abstract trait jet.MutableSet</*0*/ E : jet.Any?> : jet.Set<E>, jet.MutableCollection<E> {
     public abstract override /*1*/ fun add(/*0*/ e: E): jet.Boolean
diff --git a/jdk-annotations/java/util/annotations.xml b/jdk-annotations/java/util/annotations.xml
index 699bdbac4fd..b3eb91eac83 100644
--- a/jdk-annotations/java/util/annotations.xml
+++ b/jdk-annotations/java/util/annotations.xml
@@ -26,12 +26,12 @@
   </item>
   <item name='java.util.AbstractList java.util.ListIterator<E> listIterator()'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun listIterator() : ListIterator&lt;E&gt;&quot;"/>
+      <val name="value" val="&quot;fun listIterator() : MutableListIterator&lt;E&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.AbstractList java.util.ListIterator<E> listIterator(int)'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun listIterator(index : Int) : ListIterator&lt;E&gt;&quot;"/>
+      <val name="value" val="&quot;fun listIterator(index : Int) : MutableListIterator&lt;E&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.AbstractList E set(int, E)'>
@@ -41,7 +41,7 @@
   </item>
   <item name='java.util.AbstractList java.util.List<E> subList(int, int)'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun subList(fromIndex : Int, toIndex : Int) : List&lt;E&gt;&quot;"/>
+      <val name="value" val="&quot;fun subList(fromIndex : Int, toIndex : Int) : MutableList&lt;E&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.ArrayList boolean add(E)'>
@@ -131,12 +131,12 @@
   </item>
   <item name='java.util.List java.util.ListIterator<E> listIterator()'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun listIterator() : ListIterator&lt;E&gt;&quot;"/>
+      <val name="value" val="&quot;fun listIterator() : MutableListIterator&lt;E&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.List java.util.ListIterator<E> listIterator(int)'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun listIterator(index : Int) : ListIterator&lt;E&gt;&quot;"/>
+      <val name="value" val="&quot;fun listIterator(index : Int) : MutableListIterator&lt;E&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.List E remove(int)'>
@@ -356,12 +356,12 @@
   </item>
   <item name='java.util.HashMap java.util.Set<java.util.Map.Entry<K,V>> entrySet()'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun entrySet() : Set&lt;Map.Entry&lt;K, V&gt;&gt;&quot;"/>
+      <val name="value" val="&quot;fun entrySet() : MutableSet&lt;MutableMap.MutableEntry&lt;K, V&gt;&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.HashMap java.util.Set<K> keySet()'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun keySet() : Set&lt;K&gt;&quot;"/>
+      <val name="value" val="&quot;fun keySet() : MutableSet&lt;K&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.HashMap V put(K, V)'>
@@ -376,7 +376,7 @@
   </item>
   <item name='java.util.HashMap java.util.Collection<V> values()'>
     <annotation name='jet.runtime.typeinfo.KotlinSignature'>
-      <val name="value" val="&quot;fun values() : Collection&lt;V&gt;&quot;"/>
+      <val name="value" val="&quot;fun values() : MutableCollection&lt;V&gt;&quot;"/>
     </annotation>
   </item>
   <item name='java.util.AbstractSet boolean removeAll(java.util.Collection<?>)'>
diff --git a/js/js.libraries/src/core/javautil.kt b/js/js.libraries/src/core/javautil.kt
index c3c45cd442e..2cd02777bf2 100644
--- a/js/js.libraries/src/core/javautil.kt
+++ b/js/js.libraries/src/core/javautil.kt
@@ -52,7 +52,7 @@ public abstract class AbstractList<E>(): AbstractCollection<E>(), MutableList<E>
     override fun listIterator() : MutableListIterator<E> = js.noImpl
     override fun listIterator(index : Int) : MutableListIterator<E> = js.noImpl
 
-    override fun subList(fromIndex : Int, toIndex : Int) : List<E> = js.noImpl
+    override fun subList(fromIndex : Int, toIndex : Int) : MutableList<E> = js.noImpl
 }
 
 library
@@ -74,9 +74,9 @@ public open class HashMap<K, V>() : MutableMap<K, V> {
     public override fun remove(key : Any?) : V? = js.noImpl
     public override fun clear() : Unit = js.noImpl
     public override fun containsValue(value : Any?) : Boolean = js.noImpl
-    public override fun keySet() : Set<K> = js.noImpl
-    public override fun values() : Collection<V> = js.noImpl
-    public override fun entrySet() : Set<MutableMap.MutableEntry<K, V>> = js.noImpl
+    public override fun keySet() : MutableSet<K> = js.noImpl
+    public override fun values() : MutableCollection<V> = js.noImpl
+    public override fun entrySet() : MutableSet<MutableMap.MutableEntry<K, V>> = js.noImpl
 }
 
 library