diff --git a/src/v2/api/index.md b/src/v2/api/index.md
index eaf6b9999a..982f71e01a 100644
--- a/src/v2/api/index.md
+++ b/src/v2/api/index.md
@@ -1569,7 +1569,7 @@ type: api
 ### vm.$once( event, callback )
 
 - **Arguments:**
-  - `{string} event`
+  - `{string | Array<string>} event` (array only supported in 2.2.2+)
   - `{Function} callback`
 
 - **Usage:**