diff --git a/core/codegen/Cargo.toml b/core/codegen/Cargo.toml
index 67953ae9..6034434e 100644
--- a/core/codegen/Cargo.toml
+++ b/core/codegen/Cargo.toml
@@ -28,5 +28,5 @@ version_check = "0.9.1"
 
 [dev-dependencies]
 rocket = { version = "0.5.0-dev", path = "../lib" }
-tokio = { version = "0.2.0", features = ["io-util"] }
+tokio = { version = "0.2.9", features = ["io-util"] }
 compiletest_rs = { version = "0.3", features = ["stable"] }
diff --git a/core/codegen/src/attribute/catch.rs b/core/codegen/src/attribute/catch.rs
index 71d09455..4b6d91b8 100644
--- a/core/codegen/src/attribute/catch.rs
+++ b/core/codegen/src/attribute/catch.rs
@@ -103,6 +103,7 @@ pub fn _catch(args: TokenStream, input: TokenStream) -> Result<TokenStream> {
                     .status(#status)
                     .merge(__response)
                     .ok()
+                    .await
             })
         }
 
diff --git a/core/http/Cargo.toml b/core/http/Cargo.toml
index cf544858..6fc2701d 100644
--- a/core/http/Cargo.toml
+++ b/core/http/Cargo.toml
@@ -29,7 +29,7 @@ time = "0.2.11"
 indexmap = "1.0"
 state = "0.4"
 tokio-rustls = { version = "0.12.0", optional = true }
-tokio = { version = "0.2.0", features = ["sync", "tcp", "time"] }
+tokio = { version = "0.2.9", features = ["sync", "tcp", "time"] }
 cookie = { version = "0.14.0", features = ["percent-encode"] }
 pear = "0.1"
 unicode-xid = "0.2"
diff --git a/core/http/src/accept.rs b/core/http/src/accept.rs
index e56484fa..a8c944ec 100644
--- a/core/http/src/accept.rs
+++ b/core/http/src/accept.rs
@@ -159,7 +159,9 @@ impl PartialEq for AcceptParams {
 /// use rocket::response::Response;
 ///
 /// # #[allow(unused_variables)]
-/// let response = Response::build().header(Accept::JSON).finalize();
+/// # rocket::async_test(async {
+/// let response = Response::build().header(Accept::JSON).await;
+/// # })
 /// ```
 #[derive(Debug, Clone, PartialEq)]
 pub struct Accept(pub(crate) AcceptParams);
diff --git a/core/http/src/content_type.rs b/core/http/src/content_type.rs
index 023a4858..d3c8b954 100644
--- a/core/http/src/content_type.rs
+++ b/core/http/src/content_type.rs
@@ -39,7 +39,9 @@ use crate::ext::IntoCollection;
 /// use rocket::response::Response;
 ///
 /// # #[allow(unused_variables)]
-/// let response = Response::build().header(ContentType::HTML).finalize();
+/// # rocket::async_test(async {
+/// let response = Response::build().header(ContentType::HTML).await;
+/// # })
 /// ```
 #[derive(Debug, Clone, PartialEq, Hash)]
 pub struct ContentType(pub MediaType);
diff --git a/core/lib/Cargo.toml b/core/lib/Cargo.toml
index bb988ea0..85f19ae9 100644
--- a/core/lib/Cargo.toml
+++ b/core/lib/Cargo.toml
@@ -28,7 +28,7 @@ ctrl_c_shutdown = ["tokio/signal"]
 rocket_codegen = { version = "0.5.0-dev", path = "../codegen" }
 rocket_http = { version = "0.5.0-dev", path = "../http" }
 futures-util = "0.3.0"
-tokio = { version = "0.2.0", features = ["fs", "io-std", "io-util", "rt-threaded", "sync"] }
+tokio = { version = "0.2.9", features = ["fs", "io-std", "io-util", "rt-threaded", "sync"] }
 yansi = "0.5"
 log = { version = "0.4", features = ["std"] }
 toml = "0.4.7"
@@ -47,4 +47,4 @@ version_check = "0.9.1"
 [dev-dependencies]
 # TODO: Find a way to not depend on this.
 lazy_static = "1.0"
-tokio = { version = "0.2.0", features = ["macros"] }
+tokio = { version = "0.2.9", features = ["macros"] }
diff --git a/core/lib/src/response/content.rs b/core/lib/src/response/content.rs
index 846e20c9..1e0862a4 100644
--- a/core/lib/src/response/content.rs
+++ b/core/lib/src/response/content.rs
@@ -54,6 +54,7 @@ impl<'r, R: Responder<'r> + Send + 'r> Responder<'r> for Content<R> {
                 .merge(self.1.respond_to(req).await?)
                 .header(self.0)
                 .ok()
+                .await
         })
     }
 }
diff --git a/core/lib/src/response/debug.rs b/core/lib/src/response/debug.rs
index a11d9541..f09084b4 100644
--- a/core/lib/src/response/debug.rs
+++ b/core/lib/src/response/debug.rs
@@ -68,7 +68,7 @@ impl<'r, E: std::fmt::Debug + Send + 'r> Responder<'r> for Debug<E> {
         Box::pin(async move {
             warn_!("Debug: {:?}", Paint::default(self.0));
             warn_!("Debug always responds with {}.", Status::InternalServerError);
-            Response::build().status(Status::InternalServerError).ok()
+            Response::build().status(Status::InternalServerError).ok().await
         })
     }
 }
diff --git a/core/lib/src/response/redirect.rs b/core/lib/src/response/redirect.rs
index a1d68be0..ab64c760 100644
--- a/core/lib/src/response/redirect.rs
+++ b/core/lib/src/response/redirect.rs
@@ -155,6 +155,7 @@ impl<'r> Responder<'r> for Redirect {
                     .status(self.0)
                     .raw_header("Location", uri.to_string())
                     .ok()
+                    .await
             } else {
                 error!("Invalid URI used for redirect.");
                 Err(Status::InternalServerError)
diff --git a/core/lib/src/response/responder.rs b/core/lib/src/response/responder.rs
index b60aab81..9c78ef61 100644
--- a/core/lib/src/response/responder.rs
+++ b/core/lib/src/response/responder.rs
@@ -163,6 +163,7 @@ use crate::request::Request;
 ///                 .raw_header("X-Person-Age", self.age.to_string())
 ///                 .header(ContentType::new("application", "x-person"))
 ///                 .ok()
+///                 .await
 ///         })
 ///     }
 /// }
@@ -195,6 +196,7 @@ impl<'r> Responder<'r> for &'r str {
                 .header(ContentType::Plain)
                 .sized_body(Cursor::new(self))
                 .ok()
+                .await
         })
     }
 }
@@ -208,6 +210,7 @@ impl Responder<'_> for String {
                 .header(ContentType::Plain)
                 .sized_body(Cursor::new(self))
                 .ok()
+                .await
         })
     }
 }
@@ -221,6 +224,7 @@ impl<'r> Responder<'r> for &'r [u8] {
                 .header(ContentType::Binary)
                 .sized_body(Cursor::new(self))
                 .ok()
+                .await
         })
     }
 }
@@ -234,6 +238,7 @@ impl Responder<'_> for Vec<u8> {
                 .header(ContentType::Binary)
                 .sized_body(Cursor::new(self))
                 .ok()
+                .await
         })
     }
 }
@@ -246,8 +251,8 @@ impl Responder<'_> for File {
             let metadata = file.metadata().await;
             let stream = BufReader::new(file);
             match metadata {
-                Ok(md) => Response::build().raw_body(Body::Sized(stream, md.len())).ok(),
-                Err(_) => Response::build().streamed_body(stream).ok()
+                Ok(md) => Response::build().raw_body(Body::Sized(stream, md.len())).ok().await,
+                Err(_) => Response::build().streamed_body(stream).ok().await
             }
         })
     }
@@ -307,10 +312,10 @@ impl<'r> Responder<'r> for Status {
             match self.class() {
                 StatusClass::ClientError | StatusClass::ServerError => Err(self),
                 StatusClass::Success if self.code < 206 => {
-                    Response::build().status(self).ok()
+                    Response::build().status(self).ok().await
                 }
                 StatusClass::Informational if self.code == 100 => {
-                    Response::build().status(self).ok()
+                    Response::build().status(self).ok().await
                 }
                 _ => {
                     error_!("Invalid status used as responder: {}.", self);
diff --git a/core/lib/src/response/response.rs b/core/lib/src/response/response.rs
index 9b2c3495..24924c19 100644
--- a/core/lib/src/response/response.rs
+++ b/core/lib/src/response/response.rs
@@ -2,8 +2,9 @@ use std::{io, fmt, str};
 use std::borrow::Cow;
 use std::future::Future;
 use std::pin::Pin;
+use std::task::{Context, Poll};
 
-use tokio::io::{AsyncRead, AsyncReadExt};
+use tokio::io::{AsyncRead, AsyncReadExt, AsyncSeek, AsyncSeekExt};
 use futures_util::future::FutureExt;
 
 use crate::response::{Responder, ResultFuture};
@@ -104,6 +105,12 @@ impl<T> fmt::Debug for Body<T> {
     }
 }
 
+/// Internal workaround for `Box<dyn AsyncRead + AsyncSeek>` not being allowed.
+///
+/// https://github.com/rust-lang/rfcs/issues/2035
+trait AsyncReadAsyncSeek: AsyncRead + AsyncSeek + Unpin + Send {}
+impl<T: AsyncRead + AsyncSeek + Unpin + Send> AsyncReadAsyncSeek for T {}
+
 /// Type for easily building `Response`s.
 ///
 /// Building a [`Response`] can be a low-level ordeal; this structure presents a
@@ -117,8 +124,9 @@ impl<T> fmt::Debug for Body<T> {
 /// with field(s) modified in the `Responder` being built. These method calls
 /// can be chained: `build.a().b()`.
 ///
-/// To finish building and retrieve the built `Response`, use the
-/// [`finalize()`](#method.finalize) or [`ok()`](#method.ok) methods.
+/// To finish building and retrieve the built `Response`, `.await` the builder.
+/// The [`ok()` method](#method.ok) is also provided as a convenience
+/// for `Responder` implementations.
 ///
 /// ## Headers
 ///
@@ -153,6 +161,8 @@ impl<T> fmt::Debug for Body<T> {
 /// use rocket::response::Response;
 /// use rocket::http::{Status, ContentType};
 ///
+/// # rocket::async_test(async {
+///
 /// # #[allow(unused_variables)]
 /// let response = Response::build()
 ///     .status(Status::ImATeapot)
@@ -161,10 +171,14 @@ impl<T> fmt::Debug for Body<T> {
 ///     .raw_header("X-Teapot-Model", "Utopia")
 ///     .raw_header_adjoin("X-Teapot-Model", "Series 1")
 ///     .sized_body(Cursor::new("Brewing the best coffee!"))
-///     .finalize();
+///     .await;
+///
+/// # })
 /// ```
 pub struct ResponseBuilder<'r> {
-    response: Response<'r>
+    response: Response<'r>,
+    pending_sized_body: Option<Box<dyn AsyncReadAsyncSeek + 'r>>,
+    fut: Option<Pin<Box<dyn Future<Output=Response<'r>> + Send + 'r>>>,
 }
 
 impl<'r> ResponseBuilder<'r> {
@@ -182,7 +196,9 @@ impl<'r> ResponseBuilder<'r> {
     #[inline(always)]
     pub fn new(base: Response<'r>) -> ResponseBuilder<'r> {
         ResponseBuilder {
-            response: base
+            response: base,
+            pending_sized_body: None,
+            fut: None,
         }
     }
 
@@ -194,10 +210,14 @@ impl<'r> ResponseBuilder<'r> {
     /// use rocket::Response;
     /// use rocket::http::Status;
     ///
+    /// # rocket::async_test(async {
+    ///
     /// # #[allow(unused_variables)]
     /// let response = Response::build()
     ///     .status(Status::NotFound)
-    ///     .finalize();
+    ///     .await;
+    ///
+    /// # })
     /// ```
     #[inline(always)]
     pub fn status(&mut self, status: Status) -> &mut ResponseBuilder<'r> {
@@ -213,10 +233,13 @@ impl<'r> ResponseBuilder<'r> {
     /// ```rust
     /// use rocket::Response;
     ///
+    /// # rocket::async_test(async {
+    ///
     /// # #[allow(unused_variables)]
     /// let response = Response::build()
     ///     .raw_status(699, "Alien Encounter")
-    ///     .finalize();
+    ///     .await;
+    /// # })
     /// ```
     #[inline(always)]
     pub fn raw_status(&mut self, code: u16, reason: &'static str)
@@ -240,12 +263,16 @@ impl<'r> ResponseBuilder<'r> {
     /// use rocket::Response;
     /// use rocket::http::ContentType;
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let response = Response::build()
     ///     .header(ContentType::JSON)
     ///     .header(ContentType::HTML)
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.headers().get("Content-Type").count(), 1);
+    ///
+    /// # })
     /// ```
     #[inline(always)]
     pub fn header<'h: 'r, H>(&mut self, header: H) -> &mut ResponseBuilder<'r>
@@ -271,12 +298,16 @@ impl<'r> ResponseBuilder<'r> {
     /// use rocket::http::Header;
     /// use rocket::http::hyper::header::ACCEPT;
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let response = Response::build()
     ///     .header_adjoin(Header::new(ACCEPT.as_str(), "application/json"))
     ///     .header_adjoin(Header::new(ACCEPT.as_str(), "text/plain"))
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.headers().get("Accept").count(), 2);
+    ///
+    /// # })
     /// ```
     #[inline(always)]
     pub fn header_adjoin<'h: 'r, H>(&mut self, header: H) -> &mut ResponseBuilder<'r>
@@ -296,12 +327,16 @@ impl<'r> ResponseBuilder<'r> {
     /// ```rust
     /// use rocket::Response;
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let response = Response::build()
     ///     .raw_header("X-Custom", "first")
     ///     .raw_header("X-Custom", "second")
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.headers().get("X-Custom").count(), 1);
+    ///
+    /// # })
     /// ```
     #[inline(always)]
     pub fn raw_header<'a: 'r, 'b: 'r, N, V>(&mut self, name: N, value: V)
@@ -323,12 +358,16 @@ impl<'r> ResponseBuilder<'r> {
     /// ```rust
     /// use rocket::Response;
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let response = Response::build()
     ///     .raw_header_adjoin("X-Custom", "first")
     ///     .raw_header_adjoin("X-Custom", "second")
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.headers().get("X-Custom").count(), 2);
+    ///
+    /// # })
     /// ```
     #[inline(always)]
     pub fn raw_header_adjoin<'a: 'r, 'b: 'r, N, V>(&mut self, name: N, value: V)
@@ -339,12 +378,11 @@ impl<'r> ResponseBuilder<'r> {
         self
     }
 
-    // TODO.async: un-ignore this test once Seek/AsyncSeek situation has been resolved.
     /// Sets the body of the `Response` to be the fixed-sized `body`.
     ///
     /// # Example
     ///
-    /// ```rust,ignore
+    /// ```rust
     /// use rocket::Response;
     /// use tokio::fs::File;
     /// # use std::io;
@@ -354,15 +392,15 @@ impl<'r> ResponseBuilder<'r> {
     /// # #[allow(unused_variables)]
     /// let response = Response::build()
     ///     .sized_body(File::open("body.txt").await?)
-    ///     .finalize();
+    ///     .await;
     /// # Ok(())
     /// # }
     /// ```
     #[inline(always)]
     pub fn sized_body<B>(&mut self, body: B) -> &mut ResponseBuilder<'r>
-        where B: AsyncRead + io::Seek + Send + Unpin + 'r
+        where B: AsyncRead + AsyncSeek + Send + Unpin + 'r
     {
-        self.response.set_sized_body(body);
+        self.pending_sized_body = Some(Box::new(body));
         self
     }
 
@@ -380,7 +418,7 @@ impl<'r> ResponseBuilder<'r> {
     /// # #[allow(unused_variables)]
     /// let response = Response::build()
     ///     .streamed_body(File::open("body.txt").await?)
-    ///     .finalize();
+    ///     .await;
     /// # Ok(())
     /// # }
     /// ```
@@ -389,6 +427,7 @@ impl<'r> ResponseBuilder<'r> {
         where B: AsyncRead + Send + 'r
     {
         self.response.set_streamed_body(body);
+        self.pending_sized_body = None;
         self
     }
 
@@ -407,7 +446,7 @@ impl<'r> ResponseBuilder<'r> {
     /// # #[allow(unused_variables)]
     /// let response = Response::build()
     ///     .chunked_body(File::open("body.txt").await?, 8096)
-    ///     .finalize();
+    ///     .await;
     /// # Ok(())
     /// # }
     /// ```
@@ -416,6 +455,7 @@ impl<'r> ResponseBuilder<'r> {
             -> &mut ResponseBuilder<'r>
     {
         self.response.set_chunked_body(body, chunk_size);
+        self.pending_sized_body = None;
         self
     }
 
@@ -429,16 +469,21 @@ impl<'r> ResponseBuilder<'r> {
     /// use std::io::Cursor;
     /// use rocket::response::{Response, Body};
     ///
+    /// # rocket::async_test(async {
+    ///
     /// # #[allow(unused_variables)]
     /// let response = Response::build()
     ///     .raw_body(Body::Sized(Cursor::new("Hello!"), 6))
-    ///     .finalize();
+    ///     .await;
+    ///
+    /// # })
     /// ```
     #[inline(always)]
     pub fn raw_body<T: AsyncRead + Send + Unpin + 'r>(&mut self, body: Body<T>)
             -> &mut ResponseBuilder<'r>
     {
         self.response.set_raw_body(body);
+        self.pending_sized_body = None;
         self
     }
 
@@ -454,18 +499,20 @@ impl<'r> ResponseBuilder<'r> {
     /// use rocket::Response;
     /// use rocket::http::{Status, ContentType};
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let base = Response::build()
     ///     .status(Status::NotFound)
     ///     .header(ContentType::HTML)
     ///     .raw_header("X-Custom", "value 1")
-    ///     .finalize();
+    ///     .await;
     ///
     /// let response = Response::build()
     ///     .status(Status::ImATeapot)
     ///     .raw_header("X-Custom", "value 2")
     ///     .raw_header_adjoin("X-Custom", "value 3")
     ///     .merge(base)
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.status(), Status::NotFound);
     ///
@@ -478,9 +525,14 @@ impl<'r> ResponseBuilder<'r> {
     /// let custom_values: Vec<_> = response.headers().get("X-Custom").collect();
     /// assert_eq!(custom_values, vec!["value 1"]);
     /// # }
+    ///
+    /// # });
     /// ```
     #[inline(always)]
-    pub fn merge(&mut self, other: Response<'r>) -> &mut ResponseBuilder<'r> {
+    pub fn merge(&mut self, mut other: Response<'r>) -> &mut ResponseBuilder<'r> {
+        if other.body().is_some() {
+            self.pending_sized_body = None;
+        }
         self.response.merge(other);
         self
     }
@@ -498,18 +550,20 @@ impl<'r> ResponseBuilder<'r> {
     /// use rocket::Response;
     /// use rocket::http::{Status, ContentType};
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let other = Response::build()
     ///     .status(Status::NotFound)
     ///     .header(ContentType::HTML)
     ///     .raw_header("X-Custom", "value 1")
-    ///     .finalize();
+    ///     .await;
     ///
     /// let response = Response::build()
     ///     .status(Status::ImATeapot)
     ///     .raw_header("X-Custom", "value 2")
     ///     .raw_header_adjoin("X-Custom", "value 3")
     ///     .join(other)
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.status(), Status::ImATeapot);
     ///
@@ -522,6 +576,8 @@ impl<'r> ResponseBuilder<'r> {
     /// let custom_values: Vec<_> = response.headers().get("X-Custom").collect();
     /// assert_eq!(custom_values, vec!["value 2", "value 3", "value 1"]);
     /// # }
+    ///
+    /// # })
     /// ```
     #[inline(always)]
     pub fn join(&mut self, other: Response<'r>) -> &mut ResponseBuilder<'r> {
@@ -529,23 +585,6 @@ impl<'r> ResponseBuilder<'r> {
         self
     }
 
-    /// Retrieve the built `Response`.
-    ///
-    /// # Example
-    ///
-    /// ```rust
-    /// use rocket::Response;
-    ///
-    /// # #[allow(unused_variables)]
-    /// let response = Response::build()
-    ///     // build the response
-    ///     .finalize();
-    /// ```
-    #[inline(always)]
-    pub fn finalize(&mut self) -> Response<'r> {
-        std::mem::replace(&mut self.response, Response::new())
-    }
-
     /// Retrieve the built `Response` wrapped in `Ok`.
     ///
     /// # Example
@@ -553,15 +592,39 @@ impl<'r> ResponseBuilder<'r> {
     /// ```rust
     /// use rocket::Response;
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let response: Result<Response, ()> = Response::build()
     ///     // build the response
-    ///     .ok();
+    ///     .ok()
+    ///     .await;
     ///
     /// assert!(response.is_ok());
+    ///
+    /// # })
     /// ```
     #[inline(always)]
-    pub fn ok<T>(&mut self) -> Result<Response<'r>, T> {
-        Ok(self.finalize())
+    pub async fn ok<E>(&mut self) -> Result<Response<'r>, E> {
+        Ok(self.await)
+    }
+}
+
+impl<'r> Future for ResponseBuilder<'r> {
+    type Output = Response<'r>;
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let this = self.get_mut();
+        if this.fut.is_none() {
+            let mut response = std::mem::replace(&mut this.response, Response::new());
+            let pending_sized_body = this.pending_sized_body.take();
+            this.fut = Some(Box::pin(async {
+                if let Some(sb) = pending_sized_body {
+                    // TODO: Avoid double boxing (Pin<Box<Take<Pin<Box<dyn AsyncReadAsyncSeek>>>>>)
+                    response.set_sized_body(sb).await;
+                }
+                response
+            }));
+        }
+        this.fut.as_mut().expect("this.fut.is_none() checked and assigned Some").as_mut().poll(cx)
     }
 }
 
@@ -897,7 +960,7 @@ impl<'r> Response<'r> {
     /// let mut response = Response::new();
     /// assert!(response.body().is_none());
     ///
-    /// response.set_sized_body(Cursor::new("Hello, world!"));
+    /// response.set_sized_body(Cursor::new("Hello, world!")).await;
     /// assert_eq!(response.body_string().await, Some("Hello, world!".to_string()));
     /// # })
     /// ```
@@ -928,7 +991,7 @@ impl<'r> Response<'r> {
     /// let mut response = Response::new();
     /// assert!(response.body().is_none());
     ///
-    /// response.set_sized_body(Cursor::new("Hello, world!"));
+    /// response.set_sized_body(Cursor::new("Hello, world!")).await;
     /// assert_eq!(response.body_string().await, Some("Hello, world!".to_string()));
     /// assert!(response.body().is_none());
     /// # })
@@ -958,7 +1021,7 @@ impl<'r> Response<'r> {
     /// let mut response = Response::new();
     /// assert!(response.body().is_none());
     ///
-    /// response.set_sized_body(Cursor::new("hi!"));
+    /// response.set_sized_body(Cursor::new("hi!")).await;
     /// assert_eq!(response.body_bytes().await, Some(vec![0x68, 0x69, 0x21]));
     /// assert!(response.body().is_none());
     /// # })
@@ -987,7 +1050,7 @@ impl<'r> Response<'r> {
     /// let mut response = Response::new();
     /// assert!(response.body().is_none());
     ///
-    /// response.set_sized_body(Cursor::new("Hello, world!"));
+    /// response.set_sized_body(Cursor::new("Hello, world!")).await;
     /// assert!(response.body().is_some());
     ///
     /// let body = response.take_body();
@@ -1018,7 +1081,8 @@ impl<'r> Response<'r> {
 
     /// Sets the body of `self` to be the fixed-sized `body`. The size of the
     /// body is obtained by `seek`ing to the end and then `seek`ing back to the
-    /// start.
+    /// start. Since this is an asynchronous operation, it returns a future
+    /// and should be `await`-ed on.
     ///
     /// # Panics
     ///
@@ -1034,17 +1098,16 @@ impl<'r> Response<'r> {
     ///
     /// # rocket::async_test(async {
     /// let mut response = Response::new();
-    /// response.set_sized_body(Cursor::new("Hello, world!"));
+    /// response.set_sized_body(Cursor::new("Hello, world!")).await;
     /// assert_eq!(response.body_string().await, Some("Hello, world!".to_string()));
     /// # })
     /// ```
-    #[inline]
-    pub fn set_sized_body<B>(&mut self, mut body: B)
-        where B: AsyncRead + io::Seek + Send + Unpin + 'r
+    pub async fn set_sized_body<B>(&mut self, mut body: B)
+        where B: AsyncRead + AsyncSeek + Send + Unpin + 'r
     {
-        let size = body.seek(io::SeekFrom::End(0))
+        let size = body.seek(io::SeekFrom::End(0)).await
             .expect("Attempted to retrieve size by seeking, but failed.");
-        body.seek(io::SeekFrom::Start(0))
+        body.seek(io::SeekFrom::Start(0)).await
             .expect("Attempted to reset body by seeking after getting size.");
         self.body = Some(Body::Sized(Box::pin(body.take(size)), size));
     }
@@ -1130,18 +1193,20 @@ impl<'r> Response<'r> {
     /// use rocket::Response;
     /// use rocket::http::{Status, ContentType};
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let base = Response::build()
     ///     .status(Status::NotFound)
     ///     .header(ContentType::HTML)
     ///     .raw_header("X-Custom", "value 1")
-    ///     .finalize();
+    ///     .await;
     ///
     /// let response = Response::build()
     ///     .status(Status::ImATeapot)
     ///     .raw_header("X-Custom", "value 2")
     ///     .raw_header_adjoin("X-Custom", "value 3")
     ///     .merge(base)
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.status(), Status::NotFound);
     ///
@@ -1154,6 +1219,8 @@ impl<'r> Response<'r> {
     /// let custom_values: Vec<_> = response.headers().get("X-Custom").collect();
     /// assert_eq!(custom_values, vec!["value 1"]);
     /// # }
+    ///
+    /// # })
     /// ```
     pub fn merge(&mut self, other: Response<'r>) {
         if let Some(status) = other.status {
@@ -1179,18 +1246,20 @@ impl<'r> Response<'r> {
     /// use rocket::Response;
     /// use rocket::http::{Status, ContentType};
     ///
+    /// # rocket::async_test(async {
+    ///
     /// let other = Response::build()
     ///     .status(Status::NotFound)
     ///     .header(ContentType::HTML)
     ///     .raw_header("X-Custom", "value 1")
-    ///     .finalize();
+    ///     .await;
     ///
     /// let response = Response::build()
     ///     .status(Status::ImATeapot)
     ///     .raw_header("X-Custom", "value 2")
     ///     .raw_header_adjoin("X-Custom", "value 3")
     ///     .join(other)
-    ///     .finalize();
+    ///     .await;
     ///
     /// assert_eq!(response.status(), Status::ImATeapot);
     ///
@@ -1203,6 +1272,8 @@ impl<'r> Response<'r> {
     /// let custom_values: Vec<_> = response.headers().get("X-Custom").collect();
     /// assert_eq!(custom_values, vec!["value 2", "value 3", "value 1"]);
     /// # }
+    ///
+    /// # })
     /// ```
     pub fn join(&mut self, other: Response<'r>) {
         if self.status.is_none() {
diff --git a/core/lib/src/response/status.rs b/core/lib/src/response/status.rs
index 0bac7b13..41c85a56 100644
--- a/core/lib/src/response/status.rs
+++ b/core/lib/src/response/status.rs
@@ -175,6 +175,7 @@ impl<'r, R: Responder<'r> + Send + 'r> Responder<'r> for Created<R> {
            response.status(Status::Created)
                .raw_header("Location", self.0)
                .ok()
+               .await
         })
     }
 }
@@ -216,7 +217,7 @@ impl<'r, R: Responder<'r> + Send + 'r> Responder<'r> for Accepted<R> {
                 build.merge(responder.respond_to(req).await?);
             }
 
-            build.status(Status::Accepted).ok()
+            build.status(Status::Accepted).ok().await
         })
     }
 }
@@ -283,7 +284,7 @@ impl<'r, R: Responder<'r> + Send + 'r> Responder<'r> for BadRequest<R> {
                 build.merge(responder.respond_to(req).await?);
             }
 
-            build.status(Status::BadRequest).ok()
+            build.status(Status::BadRequest).ok().await
         })
     }
 }
@@ -390,6 +391,7 @@ impl<'r, R: Responder<'r> + Send + 'r> Responder<'r> for NotFound<R> {
             Response::build_from(self.0.respond_to(req).await?)
                 .status(Status::NotFound)
                 .ok()
+                .await
         })
     }
 }
@@ -457,6 +459,7 @@ impl<'r, R: Responder<'r> + Send + 'r> Responder<'r> for Custom<R> {
             Response::build_from(self.1.respond_to(req).await?)
                 .status(self.0)
                 .ok()
+                .await
         })
     }
 }
diff --git a/core/lib/src/response/stream.rs b/core/lib/src/response/stream.rs
index 1661a384..3f1ddd88 100644
--- a/core/lib/src/response/stream.rs
+++ b/core/lib/src/response/stream.rs
@@ -69,7 +69,7 @@ impl<T: AsyncRead> From<T> for Stream<T> {
 impl<'r, T: AsyncRead + Send + 'r> Responder<'r> for Stream<T> {
     fn respond_to(self, _: &'r Request<'_>) -> ResultFuture<'r> {
         Box::pin(async {
-            Response::build().chunked_body(self.0, self.1).ok()
+            Response::build().chunked_body(self.0, self.1).ok().await
         })
     }
 }
diff --git a/core/lib/tests/conditionally-set-server-header-996.rs b/core/lib/tests/conditionally-set-server-header-996.rs
index f5d1b533..af160970 100644
--- a/core/lib/tests/conditionally-set-server-header-996.rs
+++ b/core/lib/tests/conditionally-set-server-header-996.rs
@@ -6,10 +6,10 @@ use rocket::Response;
 use rocket::http::Header;
 
 #[get("/do_not_overwrite")]
-fn do_not_overwrite() -> Response<'static> {
+async fn do_not_overwrite() -> Response<'static> {
     Response::build()
         .header(Header::new("Server", "Test"))
-        .finalize()
+        .await
 }
 
 #[get("/use_default")]
diff --git a/examples/fairings/src/main.rs b/examples/fairings/src/main.rs
index f79aeec6..b6398b8f 100644
--- a/examples/fairings/src/main.rs
+++ b/examples/fairings/src/main.rs
@@ -54,7 +54,7 @@ impl Fairing for Counter {
                 let body = format!("Get: {}\nPost: {}", get_count, post_count);
                 response.set_status(Status::Ok);
                 response.set_header(ContentType::Plain);
-                response.set_sized_body(Cursor::new(body));
+                response.set_sized_body(Cursor::new(body)).await;
             }
         })
     }
@@ -95,7 +95,7 @@ fn rocket() -> rocket::Rocket {
             Box::pin(async move {
                 if req.uri().path() == "/" {
                     println!("    => Rewriting response body.");
-                    res.set_sized_body(Cursor::new("Hello, fairings!"));
+                    res.set_sized_body(Cursor::new("Hello, fairings!")).await;
                 }
             })
         }))