diff --git a/cohttp/connection.ml b/cohttp/connection.ml
index d19eb19c00..789292dae8 100644
--- a/cohttp/connection.ml
+++ b/cohttp/connection.ml
@@ -15,8 +15,9 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  *
  *)
+open Sexplib.Std
 
-type t = int
+type t = int with sexp
 
 let to_string = string_of_int
 
diff --git a/cohttp/connection.mli b/cohttp/connection.mli
index 01fdece5b9..a693017759 100644
--- a/cohttp/connection.mli
+++ b/cohttp/connection.mli
@@ -18,7 +18,7 @@
 
 (** Connection identifiers. *)
 
-type t
+type t with sexp
 (** Abstract type for connection identifiers. *)
 
 val create: unit -> t