diff --git a/src/monet.d.ts b/src/monet.d.ts
index e3de405..170c9c8 100644
--- a/src/monet.d.ts
+++ b/src/monet.d.ts
@@ -54,6 +54,8 @@ interface IMonad<T> extends Functor<T>, Bind<T>, Applicative<T> {
   chain<V>(fn: (val: T) => IMonad<V>): IMonad<V>;
   map<V>(fn: (val: T) => V): IMonad<V>;
   join<V>(): IMonad<V>; // only if T = IMonad<V>
+  mapT<V1, V2>(fn: (val: V1) => V2): IMonad<IMonad<V2>>; // only if T = IMonad<V1>
+  mapTT<V1, V2>(fn: (val: V1) => V2): IMonad<IMonad<IMonad<V2>>>; // only if T = IMonad<IMonad<V1>>
 
   /* These are monet-Monad-specific: */
   takeLeft(m: IMonad<T>): IMonad<T>;
diff --git a/src/monet.js b/src/monet.js
index 178f1cb..24a8d74 100644
--- a/src/monet.js
+++ b/src/monet.js
@@ -77,7 +77,7 @@
             var targetType = target[TYPE_KEY] ||
                 target.constructor && target.constructor[TYPE_KEY]
 
-            return Boolean(targetType) && 
+            return Boolean(targetType) &&
                 targetType.length >= typeName.length &&
                 targetType.indexOf(typeName) === targetType.length - typeName.length
         }
@@ -714,7 +714,7 @@
                 })
         },
         toArray: function () {
-            return this.map(function (val) { 
+            return this.map(function (val) {
                 return [val]
             }).orLazy(function () {
                 return []
@@ -1376,6 +1376,17 @@
                 })
             }
         }
+
+        type.prototype.mapT = function(fn) {
+            return this.map(function (ma) {
+                return ma.map(fn)
+            })
+        }
+        type.prototype.mapTT = function(fn) {
+            return this.map(function (ma) {
+                return ma.mapT(fn)
+            })
+        }
     }
 
     function addFunctorOps(type) {