diff --git a/docs/developers/function-file.md b/docs/developers/function-file.md
index 2684ff155..7dd9d3cc1 100644
--- a/docs/developers/function-file.md
+++ b/docs/developers/function-file.md
@@ -14,7 +14,8 @@ config:
   key2: value2
   keyN: valueN
 headers:
-  Content-Type: text/plain
+  Content-Type:
+  - text/html
 build:
 - make
 - make test