diff --git a/src/draw/text-node.h b/src/draw/text-node.h
index 2eb3c4e8..23ac4f9a 100644
--- a/src/draw/text-node.h
+++ b/src/draw/text-node.h
@@ -72,7 +72,7 @@ typedef struct {
 } MangoJumpLabel;
 
 typedef struct {
-	uint32_t type;
+	uint32_t type; // must at first in struct
 	struct wlr_scene_buffer *scene_buffer;
 	struct mango_text_buffer *buffer;
 	cairo_surface_t *surface;
diff --git a/src/ext-protocol/text-input.h b/src/ext-protocol/text-input.h
index ebe8c7b1..0eb89881 100644
--- a/src/ext-protocol/text-input.h
+++ b/src/ext-protocol/text-input.h
@@ -27,7 +27,7 @@ struct dwl_input_method_relay {
 };
 
 struct dwl_input_method_popup {
-	uint32_t type;
+	uint32_t type; // must at first in struct
 	struct wlr_input_popup_surface_v2 *popup_surface;
 	struct wlr_scene_tree *tree;
 	struct wlr_scene_tree *scene_surface;
diff --git a/src/mango.c b/src/mango.c
index 95ca4e91..b0dcbc80 100644
--- a/src/mango.c
+++ b/src/mango.c
@@ -328,7 +328,7 @@ typedef struct {
 
 struct Client {
 	/* Must keep these three elements in this order */
-	uint32_t type; /* XDGShell or X11* */
+	uint32_t type; // must at first in struct
 	struct wlr_box geom, pending, float_geom, animainit_geom,
 		overview_backup_geom, current,
 		drag_begin_geom; /* layout-relative, includes border */
@@ -509,7 +509,7 @@ typedef struct {
 
 typedef struct {
 	/* Must keep these three elements in this order */
-	uint32_t type; /* LayerShell */
+	uint32_t type; // must at first in struct
 	struct wlr_box geom, current, pending, animainit_geom;
 	Monitor *mon;
 	struct wlr_scene_tree *scene;
@@ -539,7 +539,7 @@ typedef struct {
 } LayerSurface;
 
 typedef struct {
-	uint32_t type;
+	uint32_t type; // must at first in struct
 	struct wlr_xdg_popup *wlr_popup;
 	struct wl_listener destroy;
 	struct wl_listener commit;
@@ -651,7 +651,7 @@ struct TagScrollerState {
 };
 
 typedef struct {
-	uint32_t type;
+	uint32_t type; // must at first in struct
 	int32_t orig_width;
 	int32_t orig_height;
 	bool is_subsurface;