diff --git a/lib/piaf.mli b/lib/piaf.mli
index 07b7a59..f6ee340 100644
--- a/lib/piaf.mli
+++ b/lib/piaf.mli
@@ -473,6 +473,16 @@ module Request : sig
     -> string
     -> t
 
+  val with_ :
+     ?meth:Method.t
+    -> ?target:string
+    -> ?version:Versions.HTTP.t
+    -> ?headers:Headers.t
+    -> ?scheme:Scheme.t
+    -> ?body:Body.t
+    -> t
+    -> t
+
   val uri : t -> Uri.t
   val persistent_connection : t -> bool
   val pp_hum : Format.formatter -> t -> unit [@@ocaml.toplevel_printer]
@@ -493,6 +503,14 @@ module Response : sig
     -> Status.t
     -> t
 
+  val with_ :
+     ?status:Status.t
+    -> ?headers:Headers.t
+    -> ?version:Versions.HTTP.t
+    -> ?body:Body.t
+    -> t
+    -> t
+
   val of_string :
      ?version:Versions.HTTP.t
     -> ?headers:Headers.t
diff --git a/lib/request.ml b/lib/request.ml
index 7692fbb..29a938a 100644
--- a/lib/request.ml
+++ b/lib/request.ml
@@ -49,6 +49,15 @@ let uri { scheme; target; headers; version; _ } =
 let create ~scheme ~version ?(headers = Headers.empty) ~meth ~body target =
   { meth; target; version; headers; scheme; body }
 
+let with_ ?meth ?target ?version ?headers ?scheme ?body request =
+  { meth = Option.value meth ~default:request.meth
+  ; target = Option.value target ~default:request.target
+  ; version = Option.value version ~default:request.version
+  ; headers = Option.value headers ~default:request.headers
+  ; scheme = Option.value scheme ~default:request.scheme
+  ; body = Option.value body ~default:request.body
+  }
+
 let of_http1 ?(body = Body.empty) ~scheme request =
   let { Httpaf.Request.meth; target; version; headers } = request in
   { meth
diff --git a/lib/response.ml b/lib/response.ml
index 3146d5b..2e07270 100644
--- a/lib/response.ml
+++ b/lib/response.ml
@@ -48,6 +48,13 @@ let create
   =
   { status; headers; version; body }
 
+let with_ ?status ?headers ?version ?body response =
+  { status = Option.value status ~default:response.status
+  ; version = Option.value version ~default:response.version
+  ; headers = Option.value headers ~default:response.headers
+  ; body = Option.value body ~default:response.body
+  }
+
 let of_string ?version ?headers ~body status =
   create ?version ?headers ~body:(Body.of_string body) status