diff --git a/include/wlr/types/wlr_xdg_shell.h b/include/wlr/types/wlr_xdg_shell.h
index 90371282..db1d7bd5 100644
--- a/include/wlr/types/wlr_xdg_shell.h
+++ b/include/wlr/types/wlr_xdg_shell.h
@@ -418,9 +418,11 @@ void wlr_xdg_toplevel_send_close(struct wlr_xdg_toplevel *toplevel);
 
 /**
  * Sets the parent of this toplevel. Parent can be NULL.
+ *
+ * Returns true on success, false if setting the parent would create a loop.
  */
-void wlr_xdg_toplevel_set_parent(struct wlr_xdg_toplevel *toplevel,
-		struct wlr_xdg_toplevel *parent);
+bool wlr_xdg_toplevel_set_parent(struct wlr_xdg_toplevel *toplevel,
+	struct wlr_xdg_toplevel *parent);
 
 /**
  * Request that this popup closes.
diff --git a/protocol/meson.build b/protocol/meson.build
index a6e5b465..35aee359 100644
--- a/protocol/meson.build
+++ b/protocol/meson.build
@@ -1,5 +1,5 @@
 wayland_protos = dependency('wayland-protocols',
-	version: '>=1.26',
+	version: '>=1.27',
 	fallback: 'wayland-protocols',
 	default_options: ['tests=false'],
 )
diff --git a/types/wlr_xdg_foreign_v1.c b/types/wlr_xdg_foreign_v1.c
index 8213c70b..9cca7714 100644
--- a/types/wlr_xdg_foreign_v1.c
+++ b/types/wlr_xdg_foreign_v1.c
@@ -107,6 +107,14 @@ static void xdg_imported_handle_set_parent_of(struct wl_client *client,
 	child->xdg_surface_destroy.notify = handle_child_xdg_surface_destroy;
 	child->xdg_toplevel_set_parent.notify = handle_xdg_toplevel_set_parent;
 
+	if (!wlr_xdg_toplevel_set_parent(child_toplevel, surface->toplevel)) {
+		wl_resource_post_error(surface->toplevel->resource,
+			XDG_TOPLEVEL_ERROR_INVALID_PARENT,
+			"a toplevel cannot be a parent of itself or its ancestor");
+		free(child);
+		return;
+	}
+
 	wlr_xdg_toplevel_set_parent(child_toplevel, surface->toplevel);
 	wl_signal_add(&child_toplevel->base->events.destroy,
 			&child->xdg_surface_destroy);
diff --git a/types/wlr_xdg_foreign_v2.c b/types/wlr_xdg_foreign_v2.c
index 1b79147f..43e65e0e 100644
--- a/types/wlr_xdg_foreign_v2.c
+++ b/types/wlr_xdg_foreign_v2.c
@@ -113,6 +113,14 @@ static void xdg_imported_handle_set_parent_of(struct wl_client *client,
 	child->xdg_surface_destroy.notify = handle_child_xdg_surface_destroy;
 	child->xdg_toplevel_set_parent.notify = handle_xdg_toplevel_set_parent;
 
+	if (!wlr_xdg_toplevel_set_parent(child_toplevel, surface->toplevel)) {
+		wl_resource_post_error(surface->toplevel->resource,
+			XDG_TOPLEVEL_ERROR_INVALID_PARENT,
+			"a toplevel cannot be a parent of itself or its ancestor");
+		free(child);
+		return;
+	}
+
 	wlr_xdg_toplevel_set_parent(child_toplevel, surface->toplevel);
 	wl_signal_add(&child_toplevel->base->events.destroy,
 			&child->xdg_surface_destroy);
diff --git a/types/xdg_shell/wlr_xdg_toplevel.c b/types/xdg_shell/wlr_xdg_toplevel.c
index f84f41af..420b1de4 100644
--- a/types/xdg_shell/wlr_xdg_toplevel.c
+++ b/types/xdg_shell/wlr_xdg_toplevel.c
@@ -149,16 +149,27 @@ struct wlr_xdg_toplevel *wlr_xdg_toplevel_from_resource(
 static void handle_parent_unmap(struct wl_listener *listener, void *data) {
 	struct wlr_xdg_toplevel *toplevel =
 		wl_container_of(listener, toplevel, parent_unmap);
-	wlr_xdg_toplevel_set_parent(toplevel, toplevel->parent->parent);
+	if (!wlr_xdg_toplevel_set_parent(toplevel, toplevel->parent->parent)) {
+		assert(0 && "Unreachable");
+	}
 }
 
-void wlr_xdg_toplevel_set_parent(struct wlr_xdg_toplevel *toplevel,
+bool wlr_xdg_toplevel_set_parent(struct wlr_xdg_toplevel *toplevel,
 		struct wlr_xdg_toplevel *parent) {
-	if (toplevel->parent) {
+	// Check for a loop
+	struct wlr_xdg_toplevel *iter = parent;
+	while (iter != NULL) {
+		if (iter == toplevel) {
+			return false;
+		}
+		iter = iter->parent;
+	}
+
+	if (toplevel->parent != NULL) {
 		wl_list_remove(&toplevel->parent_unmap.link);
 	}
 
-	if (parent && parent->base->mapped) {
+	if (parent != NULL && parent->base->mapped) {
 		toplevel->parent = parent;
 		toplevel->parent_unmap.notify = handle_parent_unmap;
 		wl_signal_add(&toplevel->parent->base->events.unmap,
@@ -168,6 +179,7 @@ void wlr_xdg_toplevel_set_parent(struct wlr_xdg_toplevel *toplevel,
 	}
 
 	wl_signal_emit_mutable(&toplevel->events.set_parent, NULL);
+	return true;
 }
 
 static void xdg_toplevel_handle_set_parent(struct wl_client *client,
@@ -180,7 +192,10 @@ static void xdg_toplevel_handle_set_parent(struct wl_client *client,
 		parent = wlr_xdg_toplevel_from_resource(parent_resource);
 	}
 
-	wlr_xdg_toplevel_set_parent(toplevel, parent);
+	if (!wlr_xdg_toplevel_set_parent(toplevel, parent)) {
+		wl_resource_post_error(resource, XDG_TOPLEVEL_ERROR_INVALID_PARENT,
+			"a toplevel cannot be a parent of itself or its ancestor");
+	}
 }
 
 static void xdg_toplevel_handle_set_title(struct wl_client *client,