diff --git a/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java b/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java
index 2aa14c2..2f73382 100644
--- a/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java
+++ b/user/super/com/google/gwt/emul/java/util/InternalHashCodeMap.java
@@ -103,8 +103,8 @@
 
   @Override
   public Iterator<Entry<K, V>> iterator() {
-    return new Iterator<Map.Entry<K,V>>() {
-      final InternalJsMap.Iterator<Object> chains = backingMap.entries();
+    return new Iterator<Map.Entry<K, V>>() {
+      final InternalJsMap.Iterator<?> chains = backingMap.entries();
       int itemIndex = 0;
       Entry<K, V>[] chain = newEntryChain();
       Entry<K, V> lastEntry = null;
@@ -114,8 +114,8 @@
         if (itemIndex < chain.length) {
           return true;
         }
-        InternalJsMap.IteratorEntry<Object> current = chains.next();
-        if (!current.done) {
+        InternalJsMap.IteratorEntry<?> current = chains.next();
+        if (!current.isDone()) {
           // Move to the beginning of next chain
           chain = unsafeCastToArray(current.getValue());
           itemIndex = 0;
diff --git a/user/super/com/google/gwt/emul/java/util/InternalJsMap.java b/user/super/com/google/gwt/emul/java/util/InternalJsMap.java
index 5dfbfe3..8149274 100644
--- a/user/super/com/google/gwt/emul/java/util/InternalJsMap.java
+++ b/user/super/com/google/gwt/emul/java/util/InternalJsMap.java
@@ -18,40 +18,60 @@
 import javaemul.internal.JsUtils;
 import jsinterop.annotations.JsOverlay;
 import jsinterop.annotations.JsPackage;
+import jsinterop.annotations.JsProperty;
 import jsinterop.annotations.JsType;
 
-// TODO(goktug): These classes should be interfaces with defender methods instead.
-@JsType(isNative = true, name = "Object", namespace = JsPackage.GLOBAL)
-class InternalJsMap<V> {
+@JsType(isNative = true, name = "Map", namespace = JsPackage.GLOBAL)
+interface InternalJsMap<V> {
 
-  @JsType(isNative = true, name = "Object", namespace = JsPackage.GLOBAL)
-  static class Iterator<V> {
-    public native IteratorEntry<V> next();
+  @JsType(isNative = true, name = "IteratorIterable", namespace = JsPackage.GLOBAL)
+  interface Iterator<V> {
+    IteratorEntry<V> next();
   }
 
-  @JsType(isNative = true, name = "Object", namespace = JsPackage.GLOBAL)
-  static class IteratorEntry<V> {
-    private Object[] value;
-    public boolean done;
+  // IteratorEntry<V> is the modeling for IIterableResult<Array<String|V>> as IteratorEntry<V> but
+  // java and jsinterop lack expressibility to represent this abstraction (Java does not have
+  // union types and JsInterop does not allow to map type variables). So IteratorEntry<V> ends up
+  // mapping to IIterableResult<V> which is not an accurate mapping.
+  // It is convenient to model in this way so that users of this internal class don't have to deal
+  // with the internal implementation and the mismatch is handled here with overlay methods.
+  @JsType(isNative = true, name = "IIterableResult", namespace = JsPackage.GLOBAL)
+  interface IteratorEntry<V> {
+    @JsProperty
+    boolean isDone();
+    @JsProperty(name = "value")
+    Object[] getValueInternal();
     @JsOverlay
-    public final String getKey() { return JsUtils.unsafeCastToString(value[0]); }
+    default String getKey() { return JsUtils.uncheckedCast(getValueInternal()[0]); }
     @JsOverlay
-    public final V getValue() { return (V) value[1]; }
+    default V getValue() { return JsUtils.uncheckedCast(getValueInternal()[1]); }
   }
 
-  public native V get(int key);
-  public native V get(String key);
-  public native void set(int key, V value);
-  public native void set(String key, V value);
-  @JsOverlay
-  public final void delete(int key) { JsHelper.delete(this, key); }
-  @JsOverlay
-  public final void delete(String key) { JsHelper.delete(this, key); }
-  public native Iterator<V> entries();
+  V get(int key);
+  V get(String key);
+  void set(int key, V value);
+  void set(String key, V value);
+  Iterator<V> entries();
 
-  // Calls to delete are via brackets to be compatible with old browsers where delete is keyword.
-  private static class JsHelper {
-    static native void delete(InternalJsMap obj, int key) /*-{ obj["delete"](key); }-*/;
-    static native void delete(InternalJsMap obj, String key) /*-{ obj["delete"](key); }-*/;
+  @JsOverlay
+  default void delete(int key) {
+    // Calls delete without map.delete in order to be compatible with old browsers where delete is a
+    // keyword.
+    DeleteFunction fn = JsUtils.getProperty(this, "delete");
+    fn.call(this, key);
+  }
+
+  @JsOverlay
+  default void delete(String key) {
+    // Calls delete without map.delete in order to be compatible with old browsers where delete is a
+    // keyword.
+    DeleteFunction fn = JsUtils.getProperty(this, "delete");
+    fn.call(this, key);
+  }
+
+  @JsType(isNative = true, name = "Function", namespace = JsPackage.GLOBAL)
+  interface DeleteFunction {
+    void call(InternalJsMap<?> thisArg, String key);
+    void call(InternalJsMap<?> thisArg, int key);
   }
 }
diff --git a/user/super/com/google/gwt/emul/java/util/InternalStringMap.java b/user/super/com/google/gwt/emul/java/util/InternalStringMap.java
index 3daa2af..8366f6f 100644
--- a/user/super/com/google/gwt/emul/java/util/InternalStringMap.java
+++ b/user/super/com/google/gwt/emul/java/util/InternalStringMap.java
@@ -82,21 +82,23 @@
 
   @Override
   public Iterator<Entry<K, V>> iterator() {
-    return new Iterator<Map.Entry<K,V>>() {
+    return new Iterator<Map.Entry<K, V>>() {
       InternalJsMap.Iterator<V> entries = backingMap.entries();
       InternalJsMap.IteratorEntry<V> current = entries.next();
       InternalJsMap.IteratorEntry<V> last;
 
       @Override
       public boolean hasNext() {
-        return !current.done;
+        return !current.isDone();
       }
+
       @Override
       public Entry<K, V> next() {
         last = current;
         current = entries.next();
         return newMapEntry(last, valueMod);
       }
+
       @Override
       public void remove() {
         InternalStringMap.this.remove(last.getKey());
@@ -104,14 +106,15 @@
     };
   }
 
-  private Entry<K, V> newMapEntry(final InternalJsMap.IteratorEntry<V> entry,
-      final int lastValueMod) {
+  private Entry<K, V> newMapEntry(
+      final InternalJsMap.IteratorEntry<V> entry, final int lastValueMod) {
     return new AbstractMapEntry<K, V>() {
       @SuppressWarnings("unchecked")
       @Override
       public K getKey() {
         return (K) entry.getKey();
       }
+
       @Override
       public V getValue() {
         if (valueMod != lastValueMod) {
@@ -120,6 +123,7 @@
         }
         return entry.getValue();
       }
+
       @Override
       public V setValue(V object) {
         return put(entry.getKey(), object);