diff --git a/Sources/HummingbirdCore/Response/Response.swift b/Sources/HummingbirdCore/Response/Response.swift
index f6d143576..83ba8eeca 100644
--- a/Sources/HummingbirdCore/Response/Response.swift
+++ b/Sources/HummingbirdCore/Response/Response.swift
@@ -17,7 +17,13 @@ import HTTPTypes
 /// Holds all the required to generate a HTTP Response
 public struct Response: Sendable {
     public var head: HTTPResponse
-    public var body: ResponseBody
+    public var body: ResponseBody {
+        didSet {
+            if let contentLength = body.contentLength {
+                self.head.headerFields[.contentLength] = String(describing: contentLength)
+            }
+        }
+    }
 
     public init(status: HTTPResponse.Status, headers: HTTPFields = .init(), body: ResponseBody = .init()) {
         self.head = .init(status: status, headerFields: headers)