diff --git a/mocket.js.mbt b/mocket.js.mbt
index 33de5b5..d190c5e 100644
--- a/mocket.js.mbt
+++ b/mocket.js.mbt
@@ -369,16 +369,20 @@ pub fn listen_ffi(mocket : Mocket, address : String) -> Unit {
       let responder = mocket.execute_middlewares(event, handler)
       // let boundary = "----------------moonbit-" + port.to_string()
       responder.options(event.res)
+      let safe_headers : Map[StringView, StringView] = Map([])
+      event.res.headers.each(fn(k, v) {
+        safe_headers[k] = sanitize_header_value(v.to_owned())
+      })
       res.write_head(
         event.res.status_code.to_int(),
         {
-          let headers_obj = @js.Value::from_json(event.res.headers.to_json()) catch {
+          let headers_obj = @js.Value::from_json(safe_headers.to_json()) catch {
             _ => @js.Object::new().to_value()
           }
           if !event.res.cookies.is_empty() {
             let cookies = event.res.cookies
               .values()
-              .map(fn(c) { c.to_string() })
+              .map(fn(c) { sanitize_header_value(c.to_string()) })
               .to_array()
             set_js_property(headers_obj, "Set-Cookie", array_to_js(cookies))
           }
diff --git a/mocket.native.mbt b/mocket.native.mbt
index b0c6ff0..fd2ca79 100644
--- a/mocket.native.mbt
+++ b/mocket.native.mbt
@@ -359,11 +359,13 @@ async fn send_native_response(
   conn : @http.ServerConnection,
   response : HttpResponse,
 ) -> Unit {
-  let headers = view_headers_to_strings(response.headers)
+  let raw_headers = view_headers_to_strings(response.headers)
+  let headers : Map[String, String] = Map([])
+  raw_headers.each(fn(k, v) { headers[k] = sanitize_header_value(v) })
   if !response.cookies.is_empty() {
     let cookies = response.cookies
       .values()
-      .map(cookie => cookie.to_string())
+      .map(fn(c) { sanitize_header_value(c.to_string()) })
       .to_array()
     headers.set("Set-Cookie", cookies.join("\r\nSet-Cookie: "))
   }
diff --git a/native/mongoose/mongoose.mbt b/native/mongoose/mongoose.mbt
index bb655ba..5be42e4 100644
--- a/native/mongoose/mongoose.mbt
+++ b/native/mongoose/mongoose.mbt
@@ -187,12 +187,18 @@ fn handle_request(
     )
     res.status(response.status_code.to_int())
     response.headers.each((key, value) => {
-      res.set_header(to_cbytes(key), to_cbytes(value))
+      res.set_header(
+        to_cbytes(key),
+        to_cbytes(@mocket.sanitize_header_value(value.to_owned())),
+      )
     })
     response.cookies
     .values()
     .each(cookie => {
-      res.set_header(to_cbytes("Set-Cookie"), to_cbytes(cookie.to_string()))
+      res.set_header(
+        to_cbytes("Set-Cookie"),
+        to_cbytes(@mocket.sanitize_header_value(cookie.to_string())),
+      )
     })
     res.end_bytes(response.raw_body, response.raw_body.length())
   })
diff --git a/pkg.generated.mbti b/pkg.generated.mbti
index bc31229..dfb5456 100644
--- a/pkg.generated.mbti
+++ b/pkg.generated.mbti
@@ -41,6 +41,8 @@ pub fn register_ws_connection(String, (String) -> Unit, (Bytes) -> Unit, () -> U
 
 pub fn register_ws_handler(Mocket, Int) -> Unit
 
+pub fn sanitize_header_value(String) -> String
+
 pub async fn serve_ffi(Mocket, port~ : Int) -> Unit noraise
 
 pub async fn[T, E : Error] suspend(((T) -> Unit, (E) -> Unit) -> Unit) -> T raise E
diff --git a/utils.mbt b/utils.mbt
index 3a1572f..d59ae47 100644
--- a/utils.mbt
+++ b/utils.mbt
@@ -100,6 +100,21 @@ fn parse_kv(part : BytesView, map : Map[String, String]) -> Unit {
   }
 }
 
+///|
+pub fn sanitize_header_value(s : String) -> String {
+  if !s.contains("\r") && !s.contains("\n") {
+    return s
+  }
+  let buf = StringBuilder::new()
+  for c in s {
+    match c {
+      '\r' | '\n' => ()
+      _ => buf.write_char(c)
+    }
+  }
+  buf.to_string()
+}
+
 ///|
 pub fn escape_html(s : String) -> String {
   let buf = StringBuilder::new()