diff --git a/src/rendering/hwrenderer/data/flatvertices.h b/src/rendering/hwrenderer/data/flatvertices.h
index 1a1588c710..6161cea292 100644
--- a/src/rendering/hwrenderer/data/flatvertices.h
+++ b/src/rendering/hwrenderer/data/flatvertices.h
@@ -30,6 +30,8 @@
 #include <mutex>
 
 class FRenderState;
+struct secplane_t;
+struct subsector_t;
 
 struct FFlatVertex
 {