diff --git a/doc/ITEM_SPAWN.md b/doc/ITEM_SPAWN.md
index b644f82909143..666387c19dce2 100644
--- a/doc/ITEM_SPAWN.md
+++ b/doc/ITEM_SPAWN.md
@@ -94,6 +94,7 @@ Each entry can have more values (shown above as `...`).  They allow further prop
 "container-group": "<group-id>",
 "entry-wrapper": "<item-id>",
 "sealed": <boolean>
+"custom-flags": <array of string>,
 "variant": <string>
 "artifact": <object>
 "event": <string>
@@ -108,6 +109,8 @@ Each entry can have more values (shown above as `...`).  They allow further prop
 
 `sealed`: If true, a container will be sealed when the item spawns.  Default is `true`.
 
+`custom-flags`: An array of flags that will be applied to this item.
+
 `variant`: A valid itype variant id for this item.
 
 `event`: A reference to a holiday in the `holiday` enum. If specified, the entry only spawns during the specified real holiday. This works the same way as the seasonal title screens, where the holiday is checked against the current system's time. If the holiday matches, the item's spawn probability is taken from the `prob` field. Otherwise, the spawn probability becomes 0.