diff --git a/MIGRATION.md b/MIGRATION.md
index 672aa253e..cb79e664b 100644
--- a/MIGRATION.md
+++ b/MIGRATION.md
@@ -3,9 +3,13 @@
 * Setting a cookie's SameSite property, explicitly, to `SameSite::None` will now
   result in `SameSite=None` being sent with the response Set-Cookie header.
   To create a cookie without a SameSite attribute, remove any calls setting same_site.
+
 * actix-http support for Actors messages was moved to actix-http crate and is enabled 
   with feature `actors`
 
+* `BodySize::Sized64` variant has been removed. `BodySize::Sized` now receives a
+  `u64` instead of a `usize`.
+
 ## 2.0.0
 
 * `HttpServer::start()` renamed to `HttpServer::run()`. It also possible to
diff --git a/actix-http/CHANGES.md b/actix-http/CHANGES.md
index e96b0451d..a383b6a11 100644
--- a/actix-http/CHANGES.md
+++ b/actix-http/CHANGES.md
@@ -6,6 +6,9 @@
 
 * Bump minimum supported Rust version to 1.40
 
+* `BodySize::Sized64` variant has been removed. `BodySize::Sized` now receives a
+  `u64` instead of a `usize`.
+
 ### Fixed
 
 * Support parsing of `SameSite=None` [#1503]
diff --git a/actix-http/src/body.rs b/actix-http/src/body.rs
index f887b53bb..b821e777f 100644
--- a/actix-http/src/body.rs
+++ b/actix-http/src/body.rs
@@ -15,8 +15,7 @@ use crate::error::Error;
 pub enum BodySize {
     None,
     Empty,
-    Sized(usize),
-    Sized64(u64),
+    Sized(u64),
     Stream,
 }
 
@@ -25,8 +24,7 @@ impl BodySize {
         match self {
             BodySize::None
             | BodySize::Empty
-            | BodySize::Sized(0)
-            | BodySize::Sized64(0) => true,
+            | BodySize::Sized(0) => true,
             _ => false,
         }
     }
@@ -170,7 +168,7 @@ impl MessageBody for Body {
         match self {
             Body::None => BodySize::None,
             Body::Empty => BodySize::Empty,
-            Body::Bytes(ref bin) => BodySize::Sized(bin.len()),
+            Body::Bytes(ref bin) => BodySize::Sized(bin.len() as u64),
             Body::Message(ref body) => body.size(),
         }
     }
@@ -297,7 +295,7 @@ where
 
 impl MessageBody for Bytes {
     fn size(&self) -> BodySize {
-        BodySize::Sized(self.len())
+        BodySize::Sized(self.len() as u64)
     }
 
     fn poll_next(
@@ -314,7 +312,7 @@ impl MessageBody for Bytes {
 
 impl MessageBody for BytesMut {
     fn size(&self) -> BodySize {
-        BodySize::Sized(self.len())
+        BodySize::Sized(self.len() as u64)
     }
 
     fn poll_next(
@@ -331,7 +329,7 @@ impl MessageBody for BytesMut {
 
 impl MessageBody for &'static str {
     fn size(&self) -> BodySize {
-        BodySize::Sized(self.len())
+        BodySize::Sized(self.len() as u64)
     }
 
     fn poll_next(
@@ -350,7 +348,7 @@ impl MessageBody for &'static str {
 
 impl MessageBody for Vec<u8> {
     fn size(&self) -> BodySize {
-        BodySize::Sized(self.len())
+        BodySize::Sized(self.len() as u64)
     }
 
     fn poll_next(
@@ -367,7 +365,7 @@ impl MessageBody for Vec<u8> {
 
 impl MessageBody for String {
     fn size(&self) -> BodySize {
-        BodySize::Sized(self.len())
+        BodySize::Sized(self.len() as u64)
     }
 
     fn poll_next(
@@ -458,7 +456,7 @@ where
     S: Stream<Item = Result<Bytes, Error>> + Unpin,
 {
     fn size(&self) -> BodySize {
-        BodySize::Sized64(self.size)
+        BodySize::Sized(self.size as u64)
     }
 
     /// Attempts to pull out the next value of the underlying [`Stream`].
diff --git a/actix-http/src/client/h2proto.rs b/actix-http/src/client/h2proto.rs
index 2afd2d80b..48ab9fe4a 100644
--- a/actix-http/src/client/h2proto.rs
+++ b/actix-http/src/client/h2proto.rs
@@ -64,10 +64,6 @@ where
             CONTENT_LENGTH,
             HeaderValue::try_from(format!("{}", len)).unwrap(),
         ),
-        BodySize::Sized64(len) => req.headers_mut().insert(
-            CONTENT_LENGTH,
-            HeaderValue::try_from(format!("{}", len)).unwrap(),
-        ),
     };
 
     // Extracting extra headers from RequestHeadType. HeaderMap::new() does not allocate.
diff --git a/actix-http/src/h1/encoder.rs b/actix-http/src/h1/encoder.rs
index 4689906b4..eb8c337dd 100644
--- a/actix-http/src/h1/encoder.rs
+++ b/actix-http/src/h1/encoder.rs
@@ -4,7 +4,7 @@ use std::ptr::copy_nonoverlapping;
 use std::slice::from_raw_parts_mut;
 use std::{cmp, io};
 
-use bytes::{buf::BufMutExt, BufMut, BytesMut};
+use bytes::{BufMut, BytesMut};
 
 use crate::body::BodySize;
 use crate::config::ServiceConfig;
@@ -95,15 +95,6 @@ pub(crate) trait MessageType: Sized {
                 }
             }
             BodySize::Sized(len) => helpers::write_content_length(len, dst),
-            BodySize::Sized64(len) => {
-                if camel_case {
-                    dst.put_slice(b"\r\nContent-Length: ");
-                } else {
-                    dst.put_slice(b"\r\ncontent-length: ");
-                }
-                #[allow(clippy::write_with_newline)]
-                write!(dst.writer(), "{}\r\n", len)?;
-            }
             BodySize::None => dst.put_slice(b"\r\n"),
         }
 
@@ -338,8 +329,7 @@ impl<T: MessageType> MessageEncoder<T> {
         if !head {
             self.te = match length {
                 BodySize::Empty => TransferEncoding::empty(),
-                BodySize::Sized(len) => TransferEncoding::length(len as u64),
-                BodySize::Sized64(len) => TransferEncoding::length(len),
+                BodySize::Sized(len) => TransferEncoding::length(len),
                 BodySize::Stream => {
                     if message.chunked() && !stream {
                         TransferEncoding::chunked()
@@ -582,19 +572,6 @@ mod tests {
         assert!(data.contains("Content-Type: plain/text\r\n"));
         assert!(data.contains("Date: date\r\n"));
 
-        let _ = head.encode_headers(
-            &mut bytes,
-            Version::HTTP_11,
-            BodySize::Sized64(100),
-            ConnectionType::KeepAlive,
-            &ServiceConfig::default(),
-        );
-        let data =
-            String::from_utf8(Vec::from(bytes.split().freeze().as_ref())).unwrap();
-        assert!(data.contains("Content-Length: 100\r\n"));
-        assert!(data.contains("Content-Type: plain/text\r\n"));
-        assert!(data.contains("Date: date\r\n"));
-
         let mut head = RequestHead::default();
         head.set_camel_case_headers(false);
         head.headers.insert(DATE, HeaderValue::from_static("date"));
diff --git a/actix-http/src/h2/dispatcher.rs b/actix-http/src/h2/dispatcher.rs
index b07764a03..a189697a2 100644
--- a/actix-http/src/h2/dispatcher.rs
+++ b/actix-http/src/h2/dispatcher.rs
@@ -210,10 +210,6 @@ where
                 CONTENT_LENGTH,
                 HeaderValue::try_from(format!("{}", len)).unwrap(),
             ),
-            BodySize::Sized64(len) => res.headers_mut().insert(
-                CONTENT_LENGTH,
-                HeaderValue::try_from(format!("{}", len)).unwrap(),
-            ),
         };
 
         // copy headers
diff --git a/actix-http/src/helpers.rs b/actix-http/src/helpers.rs
index ff647e72b..5ac6c9be5 100644
--- a/actix-http/src/helpers.rs
+++ b/actix-http/src/helpers.rs
@@ -30,7 +30,7 @@ pub(crate) fn write_status_line(version: Version, n: u16, bytes: &mut BytesMut)
 }
 
 /// NOTE: bytes object has to contain enough space
-pub fn write_content_length(n: usize, bytes: &mut BytesMut) {
+pub fn write_content_length(n: u64, bytes: &mut BytesMut) {
     bytes.put_slice(b"\r\ncontent-length: ");
 
     if n < 10 {
@@ -96,16 +96,16 @@ pub fn write_content_length(n: usize, bytes: &mut BytesMut) {
         bytes.put_u8(DIGITS_START + d10);
         bytes.put_u8(DIGITS_START + d1);
     } else {
-        write_usize(n, bytes);
+        write_u64(n, bytes);
     }
 
     bytes.put_slice(b"\r\n");
 }
 
-pub(crate) fn write_usize(n: usize, bytes: &mut BytesMut) {
+pub(crate) fn write_u64(n: u64, bytes: &mut BytesMut) {
     let mut n = n;
 
-    // 20 chars is max length of a usize (2^64)
+    // 20 chars is max length of a u64 (2^64)
     // digits will be added to the buffer from lsd to msd
     let mut buf = BytesMut::with_capacity(20);