diff --git a/src/lib/es2015.collection.d.ts b/src/lib/es2015.collection.d.ts
index cbc5219f5d79b..089ebdc7c662e 100644
--- a/src/lib/es2015.collection.d.ts
+++ b/src/lib/es2015.collection.d.ts
@@ -38,9 +38,22 @@ interface MapConstructor {
 declare var Map: MapConstructor;
 
 interface ReadonlyMap<K, V> {
+    /**
+     * Executes a provided function once per each key/value pair in the ReadonlyMap, in insertion order.
+     */
     forEach(callbackfn: (value: V, key: K, map: ReadonlyMap<K, V>) => void, thisArg?: any): void;
+    /**
+     * Returns a specified element from the Map object. If the value that is associated to the provided key is an object, then you will get a reference to that object and any change made to that object will effectively modify it inside the Map.
+     * @returns Returns the element associated with the specified key. If no element is associated with the specified key, undefined is returned.
+     */
     get(key: K): V | undefined;
+    /**
+     * @returns boolean indicating whether an element with the specified key exists or not.
+     */
     has(key: K): boolean;
+    /**
+     * @returns the number of elements in the Map.
+     */
     readonly size: number;
 }