diff --git a/docs/function-file.md b/docs/function-file.md
index c9cac693c..ea6ea3fc7 100644
--- a/docs/function-file.md
+++ b/docs/function-file.md
@@ -37,7 +37,7 @@ position. You may use it to override the calculated route. If you plan to use
 appended to the image as a tag.
 
 `runtime` represents programming language runtime,  for examples,
-`go`, `python3`, `java`, etc.  and the `docker` runtime when a Dockerfile exists.
+`go`, `python3`, `java`, etc.  and the `runtime` `docker` when will use the existing Dockerfile if one exists.
 
 `build` (optional) is an array of local shell calls which are used to help
 building the function.