diff --git a/src/observable/map/BaseObservableMap.ts b/src/observable/map/BaseObservableMap.ts
index aa76f641..807a11e7 100644
--- a/src/observable/map/BaseObservableMap.ts
+++ b/src/observable/map/BaseObservableMap.ts
@@ -66,7 +66,7 @@ export abstract class BaseObservableMap<K, V> extends BaseObservable<IMapObserve
         return this._defaults.join(this, ...otherMaps);
     }
 
-    mapValues(mapper: Mapper<V>, updater?: Updater<V>): MappedMap<K, V> {
+    mapValues<MappedV>(mapper: Mapper<V, MappedV>, updater?: Updater<V, MappedV>): MappedMap<K, V, MappedV> {
         return this._defaults.mapValues(this, mapper, updater);
     }
 
diff --git a/src/observable/map/BaseObservableMapTransformers.ts b/src/observable/map/BaseObservableMapTransformers.ts
index 3b39587d..b81ffe33 100644
--- a/src/observable/map/BaseObservableMapTransformers.ts
+++ b/src/observable/map/BaseObservableMapTransformers.ts
@@ -44,7 +44,7 @@ export class BaseObservableMapTransformers<K, V> {
        return new JoinedMap([_this].concat(otherMaps));
     }
 
-    mapValues(_this: BaseObservableMap<K, V>, mapper: Mapper<V>, updater?: Updater<V>): MappedMap<K, V> {
+    mapValues<MappedV>(_this: BaseObservableMap<K, V>, mapper: Mapper<V, MappedV>, updater?: Updater<V, MappedV>): MappedMap<K, V, MappedV> {
         return new MappedMap(_this, mapper, updater);
     }
 
@@ -57,12 +57,12 @@ export class BaseObservableMapTransformers<K, V> {
     }
 }
 
-export type Mapper<V> = (
+export type Mapper<V, MappedV> = (
     value: V,
     emitSpontaneousUpdate: any,
-) => V;
+) => MappedV;
 
-export type Updater<V> = (params: any, mappedValue?: V, value?: V) => void;
+export type Updater<V, MappedV> = (params: any, mappedValue?: MappedV, value?: V) => void;
 
 export type Comparator<V> = (a: V, b: V) => number;
 
diff --git a/src/observable/map/MappedMap.ts b/src/observable/map/MappedMap.ts
index bd091856..e932e1b8 100644
--- a/src/observable/map/MappedMap.ts
+++ b/src/observable/map/MappedMap.ts
@@ -23,24 +23,24 @@ import {SubscriptionHandle} from "../BaseObservable";
 so a mapped value can emit updates on it's own with this._emitSpontaneousUpdate that is passed in the mapping function
 how should the mapped value be notified of an update though? and can it then decide to not propagate the update?
 */
-export class MappedMap<K, V> extends BaseObservableMap<K, V> {
+export class MappedMap<K, V, MappedV> extends BaseObservableMap<K, MappedV> {
     private _source: BaseObservableMap<K, V>;
-    private _mapper: Mapper<V>;
-    private _updater?: Updater<V>;
-    private _mappedValues: Map<K, V>;
+    private _mapper: Mapper<V, MappedV>;
+    private _updater?: Updater<V, MappedV>;
+    private _mappedValues: Map<K, MappedV>;
     private _subscription?: SubscriptionHandle;
 
 
     constructor(
         source: BaseObservableMap<K, V>,
-        mapper: Mapper<V>,
-        updater?: Updater<V>
+        mapper: Mapper<V, MappedV>,
+        updater?: Updater<V, MappedV>
     ) {
-        super(new BaseObservableMapTransformers<K, V>());
+        super(new BaseObservableMapTransformers<K, MappedV>());
         this._source = source;
         this._mapper = mapper;
         this._updater = updater;
-        this._mappedValues = new Map<K, V>();
+        this._mappedValues = new Map<K, MappedV>();
     }
 
     _emitSpontaneousUpdate(key: K, params: any): void {
@@ -107,7 +107,7 @@ export class MappedMap<K, V> extends BaseObservableMap<K, V> {
         return this._mappedValues.size;
     }
 
-    get(key: K): V | undefined {
+    get(key: K): MappedV | undefined {
         return this._mappedValues.get(key);
     }
 }
\ No newline at end of file