diff --git a/knots/web-server.scm b/knots/web-server.scm
index cc47284..2482a79 100644
--- a/knots/web-server.scm
+++ b/knots/web-server.scm
@@ -317,7 +317,8 @@ on the procedure being called at any particular time."
             (if body-written?
                 (begin
                   (force-output client)
-                  (when (procedure? body)
+                  (when (and (procedure? body)
+                             (response-content-length response))
                     (set-port-encoding! client "ISO-8859-1"))
                   (keep-alive? response))
                 #f)))