diff --git a/src/structs.h b/src/structs.h
index 6e9e901..7acd857 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1525,6 +1525,8 @@
 
     int		class_refcount;
     int		class_copyID;		// used by garbage collection
+    class_T	*class_next_used;	// for list headed by "first_class"
+    class_T	*class_prev_used;	// for list headed by "first_class"
 
     class_T	*class_extends;		// parent class or NULL