diff --git a/include/wlr/types/wlr_xdg_shell.h b/include/wlr/types/wlr_xdg_shell.h
index 8ca3a2b1..04addfe1 100644
--- a/include/wlr/types/wlr_xdg_shell.h
+++ b/include/wlr/types/wlr_xdg_shell.h
@@ -346,7 +346,7 @@ void wlr_xdg_popup_get_toplevel_coords(struct wlr_xdg_popup *popup,
  * surface coordinate system.
  */
 void wlr_xdg_popup_unconstrain_from_box(struct wlr_xdg_popup *popup,
-		struct wlr_box *toplevel_sx_box);
+		const struct wlr_box *toplevel_sx_box);
 
 /**
   Invert the right/left anchor and gravity for this positioner. This can be
diff --git a/types/xdg_shell/wlr_xdg_popup.c b/types/xdg_shell/wlr_xdg_popup.c
index d71e6ef3..69b4cfe1 100644
--- a/types/xdg_shell/wlr_xdg_popup.c
+++ b/types/xdg_shell/wlr_xdg_popup.c
@@ -400,7 +400,7 @@ void wlr_xdg_popup_get_toplevel_coords(struct wlr_xdg_popup *popup,
 }
 
 static void xdg_popup_box_constraints(struct wlr_xdg_popup *popup,
-		struct wlr_box *toplevel_sx_box, int *offset_x, int *offset_y) {
+		const struct wlr_box *toplevel_sx_box, int *offset_x, int *offset_y) {
 	int popup_width = popup->geometry.width;
 	int popup_height = popup->geometry.height;
 	int anchor_sx = 0, anchor_sy = 0;
@@ -428,7 +428,7 @@ static void xdg_popup_box_constraints(struct wlr_xdg_popup *popup,
 }
 
 static bool xdg_popup_unconstrain_flip(struct wlr_xdg_popup *popup,
-		struct wlr_box *toplevel_sx_box) {
+		const struct wlr_box *toplevel_sx_box) {
 	int offset_x = 0, offset_y = 0;
 	xdg_popup_box_constraints(popup, toplevel_sx_box,
 		&offset_x, &offset_y);
@@ -478,7 +478,7 @@ static bool xdg_popup_unconstrain_flip(struct wlr_xdg_popup *popup,
 }
 
 static bool xdg_popup_unconstrain_slide(struct wlr_xdg_popup *popup,
-		struct wlr_box *toplevel_sx_box) {
+		const struct wlr_box *toplevel_sx_box) {
 	int offset_x = 0, offset_y = 0;
 	xdg_popup_box_constraints(popup, toplevel_sx_box,
 		&offset_x, &offset_y);
@@ -521,7 +521,7 @@ static bool xdg_popup_unconstrain_slide(struct wlr_xdg_popup *popup,
 }
 
 static bool xdg_popup_unconstrain_resize(struct wlr_xdg_popup *popup,
-		struct wlr_box *toplevel_sx_box) {
+		const struct wlr_box *toplevel_sx_box) {
 	int offset_x, offset_y;
 	xdg_popup_box_constraints(popup, toplevel_sx_box,
 		&offset_x, &offset_y);
@@ -552,7 +552,7 @@ static bool xdg_popup_unconstrain_resize(struct wlr_xdg_popup *popup,
 }
 
 void wlr_xdg_popup_unconstrain_from_box(struct wlr_xdg_popup *popup,
-		struct wlr_box *toplevel_sx_box) {
+		const struct wlr_box *toplevel_sx_box) {
 	if (xdg_popup_unconstrain_flip(popup, toplevel_sx_box)) {
 		return;
 	}