diff --git a/include/wlr/render/drm_format_set.h b/include/wlr/render/drm_format_set.h
index d7dfd779..c0192d63 100644
--- a/include/wlr/render/drm_format_set.h
+++ b/include/wlr/render/drm_format_set.h
@@ -1,3 +1,11 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
 #ifndef WLR_RENDER_DRM_FORMAT_SET_H
 #define WLR_RENDER_DRM_FORMAT_SET_H