diff --git a/test-programs/src/bin/client_post_with_body.rs b/test-programs/src/bin/client_post_with_body.rs
index ba552fa..2cbb3eb 100644
--- a/test-programs/src/bin/client_post_with_body.rs
+++ b/test-programs/src/bin/client_post_with_body.rs
@@ -8,14 +8,15 @@ struct Data {
 }
 
 fn main() {
+    let buffer = [0; 5000];
     let resp = Client::new()
         .post("https://httpbin.org/post")
-        .body("hello")
+        .body(buffer)
         .connect_timeout(Duration::from_secs(5))
         .send()
         .unwrap();
     assert_eq!(resp.status_code(), 200);
 
     let data = resp.json::<Data>().unwrap();
-    assert_eq!(data.data, "hello");
+    assert_eq!(data.data.len(), 5000);
 }
diff --git a/waki/src/body.rs b/waki/src/body.rs
index bc68184..eaf6f7a 100644
--- a/waki/src/body.rs
+++ b/waki/src/body.rs
@@ -1,5 +1,5 @@
 use crate::bindings::wasi::{
-    http::types::{IncomingBody, InputStream},
+    http::types::{IncomingBody, InputStream, OutgoingBody},
     io::streams::StreamError,
 };
 
@@ -59,3 +59,30 @@ impl Body {
         }
     }
 }
+
+pub(crate) fn write_to_outgoing_body(outgoing_body: &OutgoingBody, mut buf: &[u8]) -> Result<()> {
+    if buf.is_empty() {
+        return Ok(());
+    }
+
+    let out = outgoing_body
+        .write()
+        .map_err(|_| anyhow!("outgoing request write failed"))?;
+
+    let pollable = out.subscribe();
+    while !buf.is_empty() {
+        pollable.block();
+
+        let permit = out.check_write()?;
+        let len = buf.len().min(permit as usize);
+        let (chunk, rest) = buf.split_at(len);
+        buf = rest;
+
+        out.write(chunk)?;
+    }
+
+    out.flush()?;
+    pollable.block();
+    let _ = out.check_write()?;
+    Ok(())
+}
diff --git a/waki/src/request.rs b/waki/src/request.rs
index 255244e..eb57bb6 100644
--- a/waki/src/request.rs
+++ b/waki/src/request.rs
@@ -3,7 +3,7 @@ use crate::{
         outgoing_handler,
         types::{IncomingRequest, OutgoingBody, OutgoingRequest, RequestOptions},
     },
-    body::Body,
+    body::{write_to_outgoing_body, Body},
     header::HeaderMap,
     ErrorCode, Method, Response,
 };
@@ -241,12 +241,7 @@ impl Request {
             .body()
             .map_err(|_| anyhow!("outgoing request write failed"))?;
         let body = self.body.bytes()?;
-        if !body.is_empty() {
-            let request_body = outgoing_body
-                .write()
-                .map_err(|_| anyhow!("outgoing request write failed"))?;
-            request_body.blocking_write_and_flush(&body)?;
-        }
+        write_to_outgoing_body(&outgoing_body, body.as_slice())?;
         OutgoingBody::finish(outgoing_body, None)?;
 
         let future_response = outgoing_handler::handle(req, Some(options))?;
diff --git a/waki/src/response.rs b/waki/src/response.rs
index 0be9546..6f63a81 100644
--- a/waki/src/response.rs
+++ b/waki/src/response.rs
@@ -2,7 +2,7 @@ use crate::{
     bindings::wasi::http::types::{
         IncomingResponse, OutgoingBody, OutgoingResponse, ResponseOutparam,
     },
-    body::Body,
+    body::{write_to_outgoing_body, Body},
     header::HeaderMap,
     ErrorCode,
 };
@@ -112,14 +112,6 @@ pub fn handle_response(response_out: ResponseOutparam, response: Response) {
     ResponseOutparam::set(response_out, Ok(outgoing_response));
 
     let body = response.body.bytes().unwrap();
-    if !body.is_empty() {
-        let out = outgoing_body.write().unwrap();
-        // `blocking-write-and-flush` writes up to 4096 bytes
-        let chunks = body.chunks(4096);
-        for chunk in chunks {
-            out.blocking_write_and_flush(chunk).unwrap();
-        }
-    }
-
+    write_to_outgoing_body(&outgoing_body, body.as_slice()).unwrap();
     OutgoingBody::finish(outgoing_body, None).unwrap();
 }