diff --git a/lib_eio/buf_write.ml b/lib_eio/buf_write.ml
index e145a1e..5d26f3e 100644
--- a/lib_eio/buf_write.ml
+++ b/lib_eio/buf_write.ml
@@ -167,19 +167,6 @@ type t =
   }
 (* Invariant: [write_pos >= scheduled_pos] *)
 
-let of_buffer buffer =
-  { buffer
-  ; write_pos       = 0
-  ; scheduled_pos   = 0
-  ; scheduled       = Buffers.create 4
-  ; flushed         = Flushes.create 1
-  ; bytes_received  = 0
-  ; bytes_written   = 0
-  ; state           = Active
-  ; wake_writer     = ignore
-  ; id              = Ctf.mint_id ()
-  }
-
 exception Released
 
 let writable_exn t =
@@ -381,11 +368,25 @@ let abort t =
   in
   aux ()
 
-let create ~sw size =
-  let t = of_buffer (Bigstringaf.create size) in
+let of_buffer ~sw buffer =
+  let t = { buffer
+          ; write_pos       = 0
+          ; scheduled_pos   = 0
+          ; scheduled       = Buffers.create 4
+          ; flushed         = Flushes.create 1
+          ; bytes_received  = 0
+          ; bytes_written   = 0
+          ; state           = Active
+          ; wake_writer     = ignore
+          ; id              = Ctf.mint_id ()
+          }
+  in
   Switch.on_release sw (fun () -> abort t);
   t
 
+let create ~sw size =
+  of_buffer ~sw (Bigstringaf.create size)
+
 let pending_bytes t =
   (t.write_pos - t.scheduled_pos) + (t.bytes_received - t.bytes_written)
 
diff --git a/lib_eio/buf_write.mli b/lib_eio/buf_write.mli
index f10927a..66be8f3 100644
--- a/lib_eio/buf_write.mli
+++ b/lib_eio/buf_write.mli
@@ -268,8 +268,8 @@ val create : sw:Switch.t -> int -> t
     when [len] is not large enough to support a write.
     When [sw] is finished, any pending flush operations immediately fail. *)
 
-val of_buffer : Cstruct.buffer -> t
-(** [of_buffer buf] creates a serializer, using [buf] as its internal
+val of_buffer : sw:Switch.t -> Cstruct.buffer -> t
+(** [of_buffer ~sw buf] creates a serializer, using [buf] as its internal
     buffer. The serializer takes ownership of [buf] until the serializer has
     been closed and flushed of all output. *)