diff --git a/GLFW-4.0-sketchbook.md b/GLFW-4.0-sketchbook.md
index 97ec32c..f94931f 100644
--- a/GLFW-4.0-sketchbook.md
+++ b/GLFW-4.0-sketchbook.md
@@ -24,6 +24,7 @@
 - Unify `GLFW*proc` to `GLFWproc`
 - Sane function pointer typedefs
 - Move to enums for tokens
+- Move error callback pointer to per-thread error struct
 - Sort out `SRGB_CAPABLE` vs. `COLORSPACE`
 - Make space between last key and `GLFW_KEY_LAST`
 - Remove focus behavior from `glfwShowWindow`