diff --git a/dune-project b/dune-project
index bfc5fa3c..a21c2343 100644
--- a/dune-project
+++ b/dune-project
@@ -31,6 +31,7 @@
    (and
     (>= "1.17")
     (< "1.18")))
+  atomic
   ("jsonrpc"
    (and
     (>= "1.17")
diff --git a/linol.opam b/linol.opam
index cf1e237b..cc404cce 100644
--- a/linol.opam
+++ b/linol.opam
@@ -13,6 +13,7 @@ depends: [
   "logs"
   "trace" {>= "0.4"}
   "lsp" {>= "1.17" & < "1.18"}
+  "atomic"
   "jsonrpc" {>= "1.17" & < "1.18"}
   "ocaml" {>= "4.14"}
   "odoc" {with-doc}
diff --git a/src/dune b/src/dune
index 965dc0be..b4872003 100644
--- a/src/dune
+++ b/src/dune
@@ -3,4 +3,4 @@
  (public_name linol)
  (private_modules log)
  (flags :standard -warn-error -a+8)
- (libraries yojson lsp logs threads trace.core))
+ (libraries yojson lsp logs threads trace.core atomic))
diff --git a/src/jsonrpc2.ml b/src/jsonrpc2.ml
index 75237afd..a341bb23 100644
--- a/src/jsonrpc2.ml
+++ b/src/jsonrpc2.ml
@@ -69,7 +69,7 @@ module Make (IO : IO) : S with module IO = IO = struct
     on_sent: json -> unit;
     on_received: json -> unit;
     s: server;
-    mutable id_counter: int;
+    id_counter: int Atomic.t;
     pending_responses: (Req_id.t, server_request_handler_pair) Hashtbl.t;
   }
 
@@ -78,7 +78,7 @@ module Make (IO : IO) : S with module IO = IO = struct
       ic;
       oc;
       s = server;
-      id_counter = 0;
+      id_counter = Atomic.make 0;
       on_sent;
       on_received;
       pending_responses = Hashtbl.create 8;
@@ -116,8 +116,7 @@ module Make (IO : IO) : S with module IO = IO = struct
 
   (** Returns a new, unused [Req_id.t] to send a server request. *)
   let fresh_lsp_id (self : t) : Req_id.t =
-    let id = self.id_counter in
-    self.id_counter <- id + 1;
+    let id = Atomic.fetch_and_add self.id_counter 1 in
     `Int id
 
   (** Registers a new handler for a request response. The return indicates