diff --git a/sim/globals.ts b/sim/globals.ts
index 86201fb470..d61b245ce5 100644
--- a/sim/globals.ts
+++ b/sim/globals.ts
@@ -1037,7 +1037,7 @@ interface FormatsData extends EventMethods {
 	onAfterMega?: (this: Battle, pokemon: Pokemon) => void
 	onBegin?: (this: Battle) => void
 	onChangeSet?: (this: ModdedDex, set: PokemonSet, format: Format, setHas?: AnyObject, teamHas?: AnyObject) => string[] | void
-	onModifyTemplate?: (this: Battle, template: Template, target: Pokemon, source: Pokemon, effect: Effect) => Template | void
+	onModifyTemplate?: (this: Battle, template: Template, target?: Pokemon, source?: Pokemon, effect?: Effect) => Template | void
 	onStart?: (this: Battle) => void
 	onTeamPreview?: (this: Battle) => void
 	onValidateSet?: (this: ModdedDex, set: PokemonSet, format: Format, setHas: AnyObject, teamHas: AnyObject) => string[] | void