diff --git a/docs/content/run.md b/docs/content/run.md
index ddb99435..02494b5e 100644
--- a/docs/content/run.md
+++ b/docs/content/run.md
@@ -35,7 +35,7 @@ def app(environ, start_response):
     status = "200 OK"
     response_headers = [
         ("Content-type", "text/plain"),
-        ("Content-Length", str(len(data.md)))
+        ("Content-Length", str(len(data)))
     ]
     start_response(status, response_headers)
     return iter([data])