diff --git a/eio/angstrom_eio.ml b/eio/angstrom_eio.ml
index c001f9a..b2808a1 100644
--- a/eio/angstrom_eio.ml
+++ b/eio/angstrom_eio.ml
@@ -31,57 +31,47 @@
     POSSIBILITY OF SUCH DAMAGE.
   ----------------------------------------------------------------------------*)
 
-open Eio.Std
 open Angstrom.Buffered
 
 let default_buffer_size = 4096
 
+let default_pushback () = ()
+
 let handle_parse_result state =
   match state_to_unconsumed state with
   | None -> assert false
   | Some us -> us, state_to_result state
 
-let finalize w state =
+let finalize r state =
   (match state with
   | Done _
-   |Fail _ ->
+  | Fail _ ->
     state
   | Partial feed -> feed `Eof)
   |> handle_parse_result
-  |> Promise.resolve w
-
-class ['a] parser_sink (parser : 'a Angstrom.t) pushback =
-  let p, w = Promise.create () in
-  object
-    inherit Eio.Flow.sink
-
-    method copy src =
-      let buf = Cstruct.create default_buffer_size in
-      let rec loop = function
-        | (Done _ as state)
-         |(Fail _ as state) ->
-          finalize w state
-        | Partial feed as state -> (
-          match src#read_into buf with
-          | 0
-           |(exception End_of_file) ->
-            finalize w state
-          | len ->
-            let next = feed (`Bigstring (Bigstringaf.sub buf.buffer ~off:0 ~len)) in
-            pushback ();
-            loop next )
-      in
-      loop (parse parser)
-
-    method data = Promise.await p
-  end
-
-let default_pushback () = ()
+  |> fun x -> r := Some x
 
 let parse ?(pushback = default_pushback) parser src =
-  let sink = new parser_sink parser pushback in
-  Eio.Flow.copy src sink;
-  sink#data
+  let r = ref None in
+  let buf = Cstruct.create default_buffer_size in
+  let rec loop = function
+    | (Done _ as state)
+    | (Fail _ as state) ->
+      finalize r state
+    | Partial feed as state -> (
+      match src#read_into buf with
+      | 0
+      | (exception End_of_file) ->
+        finalize r state
+      | len ->
+        let next = feed (`Bigstring (Bigstringaf.sub buf.buffer ~off:0 ~len)) in
+        pushback ();
+        loop next )
+  in
+  loop (parse parser);
+  match !r with
+  | None -> assert false
+  | Some x -> x
 
 let rec buffered_state_loop pushback state src (buf : Cstruct.t) =
   match state with
@@ -89,7 +79,7 @@ let rec buffered_state_loop pushback state src (buf : Cstruct.t) =
     let next =
       match src#read_into buf with
       | 0
-       |(exception End_of_file) ->
+      | (exception End_of_file) ->
         k `Eof
       | len -> k (`Bigstring (Bigstringaf.sub buf.buffer ~off:0 ~len))
     in