diff --git a/include/Nazara/Graphics/AbstractViewer.hpp b/include/Nazara/Graphics/AbstractViewer.hpp
index f6fcad623..448a9ecc0 100644
--- a/include/Nazara/Graphics/AbstractViewer.hpp
+++ b/include/Nazara/Graphics/AbstractViewer.hpp
@@ -30,9 +30,9 @@ namespace Nz
 			virtual const ViewerInstance& GetViewerInstance() const = 0;
 			virtual const Recti& GetViewport() const = 0;
 
-			Vector3f Project(const Vector3f& worldPos);
+			Vector3f Project(const Vector3f& worldPos) const;
 
-			Vector3f Unproject(const Vector3f& screenPos);
+			Vector3f Unproject(const Vector3f& screenPos) const;
 	};
 }
 
diff --git a/src/Nazara/Graphics/AbstractViewer.cpp b/src/Nazara/Graphics/AbstractViewer.cpp
index 1788793c5..d7ab68bbb 100644
--- a/src/Nazara/Graphics/AbstractViewer.cpp
+++ b/src/Nazara/Graphics/AbstractViewer.cpp
@@ -11,16 +11,17 @@ namespace Nz
 {
 	AbstractViewer::~AbstractViewer() = default;
 
-	Vector3f AbstractViewer::Project(const Vector3f& worldPos)
+	Vector3f AbstractViewer::Project(const Vector3f& worldPos) const
 	{
 		const Matrix4f& viewProj = GetViewerInstance().GetViewProjMatrix();
-		Vector2f screenSize = Vector2f(GetRenderTarget().GetSize());
 
 		Vector4f clipspace = viewProj * Vector4f(worldPos, 1.f);
 		clipspace.x = clipspace.x / clipspace.w;
 		clipspace.y = clipspace.y / clipspace.w;
 		clipspace.z = clipspace.z / clipspace.w;
 
+		Vector2f screenSize = Vector2f(GetRenderTarget().GetSize());
+
 		Vector3f screenSpace;
 		screenSpace.x = (clipspace.x * 0.5f + 0.5f) * screenSize.x;
 		screenSpace.y = (clipspace.y * 0.5f + 0.5f) * screenSize.y;
@@ -29,9 +30,8 @@ namespace Nz
 		return screenSpace;
 	}
 
-	Vector3f AbstractViewer::Unproject(const Vector3f& screenPos)
+	Vector3f AbstractViewer::Unproject(const Vector3f& screenPos) const
 	{
-		const Matrix4f& inverseViewProj = GetViewerInstance().GetInvViewProjMatrix();
 		Vector2f screenSize = Vector2f(GetRenderTarget().GetSize());
 
 		// Screen space => clip space
@@ -42,6 +42,8 @@ namespace Nz
 		clipSpace.w = 1.f;
 
 		// Clip space => projection space => view space => world space
+		const Matrix4f& inverseViewProj = GetViewerInstance().GetInvViewProjMatrix();
+
 		Vector4f unproj = inverseViewProj * clipSpace;
 		return Vector3f(unproj.x, unproj.y, unproj.z) / unproj.w;
 	}