diff --git a/engine/include/sophia/handles.hpp b/engine/include/sophia/handles.hpp
index 3a97886..242535f 100644
--- a/engine/include/sophia/handles.hpp
+++ b/engine/include/sophia/handles.hpp
@@ -24,6 +24,15 @@ struct Handle {
   [[nodiscard]] auto operator<=>(const Handle&) const = default;
 };
 
+struct InvalidHandle {
+  template <typename T>
+  [[nodiscard]] constexpr operator Handle<T>() const {
+    return Handle<T>::invalid();
+  }
+};
+
+inline constexpr InvalidHandle INVALID_HANDLE{};
+
 class Mesh;
 class Panel;
 class RenderTarget;
diff --git a/examples/boids_2d/main.cpp b/examples/boids_2d/main.cpp
index 3d723fd..8dcaa57 100644
--- a/examples/boids_2d/main.cpp
+++ b/examples/boids_2d/main.cpp
@@ -1,6 +1,9 @@
 #include <algorithm>
 #include <cmath>
 #include <cstdint>
+#include <glm/glm.hpp>
+#include <glm/gtc/constants.hpp>
+#include <glm/gtc/matrix_transform.hpp>
 #include <iostream>
 #include <random>
 #include <sophia/application.hpp>
@@ -10,12 +13,6 @@
 #include <string>
 #include <vector>
 
-#define GLM_FORCE_RADIANS
-#define GLM_FORCE_DEPTH_ZERO_TO_ONE
-#include <glm/glm.hpp>
-#include <glm/gtc/constants.hpp>
-#include <glm/gtc/matrix_transform.hpp>
-
 struct Boid {
   glm::vec2 position;
   glm::vec2 velocity;