diff --git a/CHANGES.md b/CHANGES.md
index 145caec1..375f2882 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -19,6 +19,8 @@
 
 * Websocket server finished() isn't called if client disconnects #511
 
+* Responses with the following codes: 100, 101, 102, 204 -- are sent without Content-Length header. #521
+
 
 ## [0.7.8] - 2018-09-17
 
diff --git a/src/server/output.rs b/src/server/output.rs
index 46b03c9d..70c24fac 100644
--- a/src/server/output.rs
+++ b/src/server/output.rs
@@ -11,7 +11,7 @@ use flate2::write::{GzEncoder, ZlibEncoder};
 #[cfg(feature = "flate2")]
 use flate2::Compression;
 use http::header::{ACCEPT_ENCODING, CONTENT_LENGTH};
-use http::Version;
+use http::{StatusCode, Version};
 
 use super::message::InnerRequest;
 use body::{Binary, Body};
@@ -192,7 +192,13 @@ impl Output {
         let transfer = match resp.body() {
             Body::Empty => {
                 if !info.head {
-                    info.length = ResponseLength::Zero;
+                    info.length = match resp.status() {
+                        StatusCode::NO_CONTENT
+                        | StatusCode::CONTINUE
+                        | StatusCode::SWITCHING_PROTOCOLS
+                        | StatusCode::PROCESSING => ResponseLength::None,
+                        _ => ResponseLength::Zero,
+                    };
                 }
                 *self = Output::Empty(buf);
                 return;