diff --git a/README.md b/README.md
index 79505d3..0f1a160 100644
--- a/README.md
+++ b/README.md
@@ -149,6 +149,43 @@ In the example above, a child injector is created. It can provide values for the
 The `rootInjector` always remains stateless. So don't worry about reusing it in your tests or reusing it for different parts of your application. However,
 any ChildInjector _is stateful_. For example, it can [cache the injected value](#-control-lifecycle) or [keep track of stuff to dispose](#-disposing-provided-stuff)
 
+## 🎄 Decorate your dependencies
+
+A common use case for dependency injection is the [decorator design pattern](https://en.wikipedia.org/wiki/Decorator_pattern). It is used to dynamically add functionality to existing dependencies. Typed inject supports decoration of existing dependencies using its `provideFactory` and `provideClass` methods.
+
+```ts
+import { tokens, rootInjector } from 'typed-inject';
+
+class Foo {
+  public bar() {
+    console.log ('bar!');
+  }
+}
+
+function fooDecorator(foo: Foo) {
+  return {
+    bar() {
+      console.log('before call');
+      foo.bar();
+      console.log('after call');
+    }
+  };
+}
+fooDecorator.inject = tokens('foo');
+
+const fooProvider = rootInjector
+  .provideClass('foo', Foo)
+  .provideFactory('foo', fooDecorator);
+const foo = fooProvider.resolve('foo');
+
+foo.bar();
+// => "before call"
+// => "bar!"
+// => "after call"
+```
+
+In this example above the `Foo` class is decorated by the `fooDecorator`.
+
 ## ♻ Control lifecycle
 
 You can determine the lifecycle of dependencies with the third `Scope` parameter of `provideFactory` and `provideClass` methods.
diff --git a/src/InjectorImpl.ts b/src/InjectorImpl.ts
index 6f8db04..74a50fe 100644
--- a/src/InjectorImpl.ts
+++ b/src/InjectorImpl.ts
@@ -5,6 +5,7 @@ import { Injector } from './api/Injector';
 import { Exception } from './Exception';
 import { Disposable } from './api/Disposable';
 import { isDisposable } from './utils';
+import { TChildContext } from './api/TChildContext';
 
 const DEFAULT_SCOPE = Scope.Singleton;
 
@@ -64,16 +65,17 @@ abstract class AbstractInjector<TContext> implements Injector<TContext>  {
     });
   }
 
-  public provideValue<Token extends string, R>(token: Token, value: R): AbstractInjector<{ [k in Token]: R; } & TContext> {
+  public provideValue<Token extends string, R>(token: Token, value: R)
+    : AbstractInjector<TChildContext<TContext, R, Token>> {
     return new ValueProvider(this, token, value);
   }
 
   public provideClass<Token extends string, R, Tokens extends InjectionToken<TContext>[]>(token: Token, Class: InjectableClass<TContext, R, Tokens>, scope = DEFAULT_SCOPE)
-    : AbstractInjector<{ [k in Token]: R; } & TContext> {
+    : AbstractInjector<TChildContext<TContext, R, Token>> {
     return new ClassProvider(this, token, scope, Class);
   }
   public provideFactory<Token extends string, R, Tokens extends InjectionToken<TContext>[]>(token: Token, factory: InjectableFunction<TContext, R, Tokens>, scope = DEFAULT_SCOPE)
-    : AbstractInjector<{ [k in Token]: R; } & TContext> {
+    : AbstractInjector<TChildContext<TContext, R, Token>> {
     return new FactoryProvider(this, token, scope, factory);
   }
 
@@ -96,9 +98,7 @@ class RootInjector extends AbstractInjector<{}> {
   }
 }
 
-type ChildContext<TParentContext, TProvided, CurrentToken extends string> = TParentContext & { [K in CurrentToken]: TProvided };
-
-abstract class ChildInjector<TParentContext, TProvided, CurrentToken extends string> extends AbstractInjector<ChildContext<TParentContext, TProvided, CurrentToken>> {
+abstract class ChildInjector<TParentContext, TProvided, CurrentToken extends string> extends AbstractInjector<TChildContext<TParentContext, TProvided, CurrentToken>> {
 
   private cached: { value?: any } | undefined;
   private readonly disposables = new Set<Disposable>();
@@ -114,16 +114,18 @@ abstract class ChildInjector<TParentContext, TProvided, CurrentToken extends str
 
   protected isDisposed = false;
 
-  public injectClass<R, Tokens extends InjectionToken<ChildContext<TParentContext, TProvided, CurrentToken>>[]>(Class: InjectableClass<ChildContext<TParentContext, TProvided, CurrentToken>, R, Tokens>, providedIn?: Function): R {
+  public injectClass
+    <R, Tokens extends InjectionToken<TChildContext<TParentContext, TProvided, CurrentToken>>[]>(Class: InjectableClass<TChildContext<TParentContext, TProvided, CurrentToken>, R, Tokens>, providedIn?: Function): R {
     this.throwIfDisposed(Class);
     return super.injectClass(Class, providedIn);
   }
-  public injectFunction<R, Tokens extends InjectionToken<ChildContext<TParentContext, TProvided, CurrentToken>>[]>(fn: InjectableFunction<ChildContext<TParentContext, TProvided, CurrentToken>, R, Tokens>, providedIn?: Function): R {
+  public injectFunction
+    <R, Tokens extends InjectionToken<TChildContext<TParentContext, TProvided, CurrentToken>>[]>(fn: InjectableFunction<TChildContext<TParentContext, TProvided, CurrentToken>, R, Tokens>, providedIn?: Function): R {
     this.throwIfDisposed(fn);
     return super.injectFunction(fn, providedIn);
   }
 
-  public resolve<Token extends keyof ChildContext<TParentContext, TProvided, CurrentToken>>(token: Token, target?: Function): ChildContext<TParentContext, TProvided, CurrentToken>[Token] {
+  public resolve<Token extends keyof TChildContext<TParentContext, TProvided, CurrentToken>>(token: Token, target?: Function): TChildContext<TParentContext, TProvided, CurrentToken>[Token] {
     this.throwIfDisposed(token);
     return super.resolve(token, target);
   }
@@ -155,19 +157,15 @@ abstract class ChildInjector<TParentContext, TProvided, CurrentToken extends str
     await Promise.all(promisesToAwait);
   }
 
-  protected resolveInternal<SearchToken extends keyof ChildContext<TParentContext, TProvided, CurrentToken>>(token: SearchToken, target: Function | undefined)
-    : ChildContext<TParentContext, TProvided, CurrentToken>[SearchToken] {
+  protected resolveInternal<SearchToken extends keyof TChildContext<TParentContext, TProvided, CurrentToken>>(token: SearchToken, target: Function | undefined)
+    : TChildContext<TParentContext, TProvided, CurrentToken>[SearchToken] {
     if (token === this.token) {
       if (this.cached) {
         return this.cached.value as any;
       } else {
         const value = this.result(target);
-        if (this.responsibleForDisposing && isDisposable(value)) {
-          this.disposables.add(value);
-        }
-        if (this.scope === Scope.Singleton) {
-          this.cached = { value };
-        }
+        this.addToDisposablesIfNeeded(value);
+        this.addToCacheIfNeeded(value);
         return value as any;
       }
     } else {
@@ -175,6 +173,18 @@ abstract class ChildInjector<TParentContext, TProvided, CurrentToken extends str
     }
   }
 
+  private addToCacheIfNeeded(value: TProvided) {
+    if (this.scope === Scope.Singleton) {
+      this.cached = { value };
+    }
+  }
+
+  private addToDisposablesIfNeeded(value: TProvided) {
+    if (this.responsibleForDisposing && isDisposable(value)) {
+      this.disposables.add(value);
+    }
+  }
+
 }
 
 class ValueProvider<TParentContext, TProvided, ProvidedToken extends string> extends ChildInjector<TParentContext, TProvided, ProvidedToken> {
@@ -196,7 +206,7 @@ class FactoryProvider<TParentContext, TProvided, ProvidedToken extends string, T
     super(parent, token, scope);
   }
   protected result(target: Function): TProvided {
-    return this.injectFunction(this.injectable as any, target);
+    return this.parent.injectFunction(this.injectable, target);
   }
   protected readonly responsibleForDisposing = true;
 }
@@ -209,9 +219,9 @@ class ClassProvider<TParentContext, TProvided, ProvidedToken extends string, Tok
     super(parent, token, scope);
   }
   protected result(target: Function): TProvided {
-    return this.injectClass(this.injectable as any, target);
+    return this.parent.injectClass(this.injectable, target);
   }
   protected readonly responsibleForDisposing = true;
 }
 
-export const rootInjector = new RootInjector() as Injector<{}>;
+export const rootInjector: Injector<{}> = new RootInjector();
diff --git a/src/api/Injector.ts b/src/api/Injector.ts
index 5eb3c9b..934275c 100644
--- a/src/api/Injector.ts
+++ b/src/api/Injector.ts
@@ -1,15 +1,17 @@
 import { InjectableClass, InjectableFunction } from './Injectable';
 import { InjectionToken } from './InjectionToken';
 import { Scope } from './Scope';
+import { TChildContext } from './TChildContext';
 
 export interface Injector<TContext = {}> {
   injectClass<R, Tokens extends InjectionToken<TContext>[]>(Class: InjectableClass<TContext, R, Tokens>): R;
   injectFunction<R, Tokens extends InjectionToken<TContext>[]>(Class: InjectableFunction<TContext, R, Tokens>): R;
   resolve<Token extends keyof TContext>(token: Token): TContext[Token];
-  provideValue<Token extends string, R>(token: Token, value: R): Injector<{ [k in Token]: R } & TContext>;
+  provideValue<Token extends string, R>(token: Token, value: R)
+    : Injector<TChildContext<TContext, R, Token>>;
   provideClass<Token extends string, R, Tokens extends InjectionToken<TContext>[]>(token: Token, Class: InjectableClass<TContext, R, Tokens>, scope?: Scope)
-    : Injector<{ [k in Token]: R } & TContext>;
+    : Injector<TChildContext<TContext, R, Token>>;
   provideFactory<Token extends string, R, Tokens extends InjectionToken<TContext>[]>(token: Token, factory: InjectableFunction<TContext, R, Tokens>, scope?: Scope)
-    : Injector<{ [k in Token]: R } & TContext>;
+    : Injector<TChildContext<TContext, R, Token>>;
   dispose(): Promise<void>;
 }
diff --git a/src/api/TChildContext.ts b/src/api/TChildContext.ts
new file mode 100644
index 0000000..8054251
--- /dev/null
+++ b/src/api/TChildContext.ts
@@ -0,0 +1,3 @@
+export type TChildContext<TParentContext, TProvided, CurrentToken extends string> = {
+  [K in keyof (TParentContext & { [K in CurrentToken]: TProvided })]: K extends CurrentToken ? TProvided : K extends keyof TParentContext ? TParentContext[K]: never;
+};
diff --git a/src/index.ts b/src/index.ts
index de8eff2..f34a7bc 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,6 +3,7 @@ export * from './api/CorrespondingType';
 export * from './api/InjectionToken';
 export * from './api/Injector';
 export * from './api/Scope';
+export * from './api/TChildContext';
 export * from './InjectorImpl';
 export * from './tokens';
 export * from './api/Disposable';
diff --git a/test/unit/Injector.spec.ts b/test/unit/Injector.spec.ts
index 5bf42b3..c0a27bc 100644
--- a/test/unit/Injector.spec.ts
+++ b/test/unit/Injector.spec.ts
@@ -248,6 +248,28 @@ describe('InjectorImpl', () => {
       expect(() => sut.injectClass(class Bar { })).throws('Injector is already disposed. Please don\'t use it anymore. Tried to inject "Bar".');
       expect(() => sut.injectFunction(function baz() { })).throws('Injector is already disposed. Please don\'t use it anymore. Tried to inject "baz".');
     });
+
+    it('should be able to decorate an existing token', () => {
+      function incrementDecorator(n: number) {
+        return ++n;
+      }
+      incrementDecorator.inject = tokens('answer');
+
+      const answerProvider = rootInjector.provideValue('answer', 40)
+        .provideFactory('answer', incrementDecorator)
+        .provideFactory('answer', incrementDecorator);
+
+      expect(answerProvider.resolve('answer')).eq(42);
+      expect(answerProvider.resolve('answer')).eq(42);
+    });
+
+    it('should be able to change the type of a token', () => {
+      const answerProvider = rootInjector
+        .provideValue('answer', 42)
+        .provideValue('answer', '42');
+      expect(answerProvider.resolve('answer')).eq('42');
+      expect(typeof answerProvider.resolve('answer')).eq('string');
+    });
   });
 
   describe('ClassProvider', () => {
@@ -258,9 +280,26 @@ describe('InjectorImpl', () => {
       expect(() => sut.injectClass(class Bar { })).throws('Injector is already disposed. Please don\'t use it anymore. Tried to inject "Bar".');
       expect(() => sut.injectFunction(function baz() { })).throws('Injector is already disposed. Please don\'t use it anymore. Tried to inject "baz".');
     });
+
+    it('should be able to decorate an existing token', () => {
+      class Foo {
+        public static inject = tokens('answer');
+        constructor(innerFoo: { answer: number }) {
+          this.answer = innerFoo.answer + 1;
+        }
+        public answer: number;
+      }
+
+      const answerProvider = rootInjector.provideValue('answer', { answer: 40 })
+        .provideClass('answer', Foo)
+        .provideClass('answer', Foo);
+
+      expect(answerProvider.resolve('answer').answer).eq(42);
+    });
+
   });
 
-  describe('dispose', () => {
+  describe(rootInjector.dispose.name, () => {
 
     it('should dispose all disposable singleton dependencies', async () => {
       // Arrange
diff --git a/testResources/override-token-should-change-type.ts b/testResources/override-token-should-change-type.ts
new file mode 100644
index 0000000..aefc75a
--- /dev/null
+++ b/testResources/override-token-should-change-type.ts
@@ -0,0 +1,9 @@
+// error: "Type 'string' is not assignable to type 'number'"
+
+import { rootInjector } from '../src/index';
+
+const fooProvider = rootInjector
+  .provideValue('foo', 42)
+  .provideValue('foo', 'bar');
+
+const foo: number = fooProvider.resolve('foo');
diff --git a/testResources/tokens-of-type-string.ts b/testResources/tokens-of-type-string.ts
index a93db81..366bd14 100644
--- a/testResources/tokens-of-type-string.ts
+++ b/testResources/tokens-of-type-string.ts
@@ -1,4 +1,4 @@
-// error: "Type 'string[]' is not assignable to type 'InjectionToken<{ bar: number; }>[]"
+// error: "Type 'string[]' is not assignable to type 'InjectionToken<TChildContext<{}, number, \"bar\">>[]'"
 
 import { rootInjector } from '../src/index';