diff --git a/include/file.h b/include/file.h
index d1ffcf55..bf2c2bc7 100644
--- a/include/file.h
+++ b/include/file.h
@@ -60,7 +60,9 @@ struct empfile {
  *
  * EFF_XY and EFF_GROUP assert that coordinates / group of such a
  * file's record can be safely obtained by dereferencing its memory
- * address cast to struct genitem *
+ * address cast to struct genitem *.
+ *
+ * EFF_OWNER asserts that player->owner is set by ef_read().
  */
 #define EFF_XY		bit(0)	/* has location */
 #define EFF_MEM		bit(1)	/* stored entirely in-memory */