diff --git a/src/slic3r/GUI/Camera.cpp b/src/slic3r/GUI/Camera.cpp
index 00fac429da..682f15b310 100644
--- a/src/slic3r/GUI/Camera.cpp
+++ b/src/slic3r/GUI/Camera.cpp
@@ -43,8 +43,6 @@ void Camera::set_type(EType type)
         m_type = type;
         if (m_update_config_on_type_change_enabled)
             wxGetApp().app_config->set("use_perspective_camera", (m_type == EType::Perspective) ? "1" : "0");
-
-        update_projection();
     }
 }
 
@@ -605,37 +603,6 @@ void Camera::update_zenit()
     m_zenit = Geometry::rad2deg(0.5 * M_PI - std::acos(std::clamp(-get_dir_forward().dot(Vec3d::UnitZ()), -1.0, 1.0)));
 }
 
-void Camera::update_projection()
-{
-    double w = 0.5 * (double)m_viewport[2];
-    double h = 0.5 * (double)m_viewport[3];
-
-    const double inv_zoom = get_inv_zoom();
-    w *= inv_zoom;
-    h *= inv_zoom;
-
-    switch (m_type)
-    {
-    default:
-    case EType::Ortho:
-    {
-        m_gui_scale = 1.0;
-        break;
-    }
-    case EType::Perspective:
-    {
-        // scale near plane to keep w and h constant on the plane at z = m_distance
-        const double scale = m_frustrum_zs.first / m_distance;
-        w *= scale;
-        h *= scale;
-        m_gui_scale = scale;
-        break;
-    }
-    }
-
-    apply_projection(-w, w, -h, h, m_frustrum_zs.first, m_frustrum_zs.second);
-}
-
 } // GUI
 } // Slic3r
 
diff --git a/src/slic3r/GUI/Camera.hpp b/src/slic3r/GUI/Camera.hpp
index 057892353f..e8915f1a5c 100644
--- a/src/slic3r/GUI/Camera.hpp
+++ b/src/slic3r/GUI/Camera.hpp
@@ -157,7 +157,6 @@ private:
     void set_default_orientation();
     Vec3d validate_target(const Vec3d& target) const;
     void update_zenit();
-    void update_projection();
 };
 
 } // GUI
diff --git a/src/slic3r/GUI/GLCanvas3D.cpp b/src/slic3r/GUI/GLCanvas3D.cpp
index 51d56fa996..7203247c3c 100644
--- a/src/slic3r/GUI/GLCanvas3D.cpp
+++ b/src/slic3r/GUI/GLCanvas3D.cpp
@@ -6996,13 +6996,29 @@ Vec3d GLCanvas3D::_mouse_to_3d(const Point& mouse_pos, const float* z, bool use_
     else {
         Camera& camera = wxGetApp().plater()->get_camera();
         const Camera::EType type = camera.get_type();
-        if (use_ortho)
-            camera.set_type(Camera::EType::Ortho);
         const Vec4i viewport(camera.get_viewport().data());
+        Transform3d projection_matrix;
+        if (use_ortho && type != Camera::EType::Ortho) {
+            const double inv_zoom = camera.get_inv_zoom();
+            const double left   = -0.5 * inv_zoom * double(viewport[2]);
+            const double bottom = -0.5 * inv_zoom * double(viewport[3]);
+            const double right  = 0.5 * inv_zoom * double(viewport[2]);
+            const double top    = 0.5 * inv_zoom * double(viewport[3]);
+            const double near_z = camera.get_near_z();
+            const double far_z  = camera.get_far_z();
+            const double inv_dx = 1.0 / (right - left);
+            const double inv_dy = 1.0 / (top - bottom);
+            const double inv_dz = 1.0 / (far_z - near_z);
+            projection_matrix.matrix() << 2.0 * near_z * inv_dx, 0.0, (left + right) * inv_dx, 0.0,
+                0.0, 2.0 * near_z * inv_dy, (bottom + top) * inv_dy, 0.0,
+                0.0, 0.0, -(near_z + far_z) * inv_dz, -2.0 * near_z * far_z * inv_dz,
+                0.0, 0.0, -1.0, 0.0;
+        }
+        else
+            projection_matrix = camera.get_projection_matrix();
+
         Vec3d out;
-        igl::unproject(Vec3d(mouse_pos.x(), viewport[3] - mouse_pos.y(), *z), camera.get_view_matrix().matrix(), camera.get_projection_matrix().matrix(), viewport, out);
-        if (use_ortho)
-            camera.set_type(type);
+        igl::unproject(Vec3d(mouse_pos.x(), viewport[3] - mouse_pos.y(), *z), camera.get_view_matrix().matrix(), projection_matrix.matrix(), viewport, out);
         return out;
     }
 }