diff --git a/src/back.ts b/src/back.ts
index 092b5d2..a32d352 100644
--- a/src/back.ts
+++ b/src/back.ts
@@ -367,7 +367,7 @@ class Session {
 				json: {
 					i: config.i,
 					text: text,
-					renoteId: renote ? renote.id : null
+					renoteId: renote ? renote.id : undefined
 				}
 			});