diff --git a/src/structs.h b/src/structs.h
index 50260ae..5b3f566 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1487,6 +1487,7 @@
 {
     char_u	*class_name;		// allocated
     int		class_refcount;
+    int		class_copyID;		// used by garbage collection
 
     // class members: "static varname"
     int		class_class_member_count;