diff --git a/src/inputsystem/inputstacksystem.cpp b/src/inputsystem/inputstacksystem.cpp
index 723a22a1..bc3b8422 100644
--- a/src/inputsystem/inputstacksystem.cpp
+++ b/src/inputsystem/inputstacksystem.cpp
@@ -216,36 +216,35 @@ void CInputStackSystem::UpdateCursorState()
 	}
 }
 
-//-----------------------------------------------------------------------------
-// Get dependencies
-//-----------------------------------------------------------------------------
-//static AppSystemInfo_t s_Dependencies[] =
-//{
-//	{ "inputsystem" DLL_EXT_STRING, INPUTSYSTEM_INTERFACE_VERSION },
-//	{ NULL, NULL }
-//};
-//
-//const AppSystemInfo_t* CInputStackSystem::GetDependencies()
-//{
-//	return s_Dependencies;
-//}
-
-
 //-----------------------------------------------------------------------------
 // Shutdown
 //-----------------------------------------------------------------------------
-//void CInputStackSystem::Shutdown()
-//{
-//	// Delete any leaked contexts
-//	while( m_ContextStack.Count() )
-//	{
-//		InputContext_t *pContext = NULL;
-//		m_ContextStack.Pop( pContext );
-//		delete pContext;
-//	}
-//
-//	BaseClass::Shutdown();
-//}
+void CInputStackSystem::Shutdown()
+{
+	// Delete any leaked contexts
+	while( m_ContextStack.Count() )
+	{
+		InputContext_t *pContext = NULL;
+		m_ContextStack.Pop( pContext );
+		delete pContext;
+	}
+
+	BaseClass::Shutdown();
+}
+
+//-----------------------------------------------------------------------------
+// Get dependencies
+//-----------------------------------------------------------------------------
+static AppSystemInfo_t s_Dependencies[] =
+{
+	{ "inputsystem" DLL_EXT_STRING, INPUTSYSTEM_INTERFACE_VERSION },
+	{ NULL, NULL }
+};
+
+const AppSystemInfo_t* CInputStackSystem::GetDependencies()
+{
+	return s_Dependencies;
+}
 
 //-----------------------------------------------------------------------------
 // Singleton instance
diff --git a/src/inputsystem/inputstacksystem.h b/src/inputsystem/inputstacksystem.h
index 1c4d8455..b8e888da 100644
--- a/src/inputsystem/inputstacksystem.h
+++ b/src/inputsystem/inputstacksystem.h
@@ -30,13 +30,9 @@ class CInputStackSystem : public CTier1AppSystem< IInputStackSystem >
 	typedef CTier1AppSystem< IInputStackSystem > BaseClass;
 
 	// Methods of IAppSystem
-	// NOTE: currently, the implementation in the game engine is used. If the
-	// vtable ever gets swapped with the implementation in the SDK, make sure
-	// to implement BaseClass::Shutdown() and uncomment the functions below !!!
-	// The implementation in this SDK is identical to that of the engine.
 public:
-	//virtual const AppSystemInfo_t* GetDependencies();
-	//virtual void Shutdown();
+	virtual void Shutdown();
+	virtual const AppSystemInfo_t* GetDependencies();
 
 	// Methods of IInputStackSystem
 public:
@@ -56,6 +52,13 @@ private:
 	CUtlStack< InputContext_t* > m_ContextStack;
 };
 
+// NOTE: we use the engine's implementation of CInputStackSystem, even though
+// we have the entire class implemented in the SDK. If, for whatever reason,
+// the SDK's implementation is used, make sure all methods are tested properly
+// first before fully migrating to the SDK's implementation. The only method
+// that appeared to have changed compared to other source game interfaces is
+// CInputStackSystem::PopInputContext(), which now actually takes the context
+// handle to pop it rather than pushing/popping handles in an explicit order.
 extern CInputStackSystem* g_pInputStackSystem;
 
 ///////////////////////////////////////////////////////////////////////////////