diff --git a/packages/frontend/src/components/MkPostForm.vue b/packages/frontend/src/components/MkPostForm.vue
index 0de15f2eb8..f610569f6d 100644
--- a/packages/frontend/src/components/MkPostForm.vue
+++ b/packages/frontend/src/components/MkPostForm.vue
@@ -423,7 +423,7 @@ function addVisibleUser() {
 	os.selectUser().then(user => {
 		pushVisibleUser(user);
 
-		if (!text.includes(`@${user.username}`)) {
+		if (!text.toLowerCase().includes(`@${user.username.toLowerCase()}`)) {
 			text = `@${Acct.toString(user)} ${text}`;
 		}
 	});