diff --git a/src/client/batch.ml b/src/client/batch.ml
index be4d7c46..ba17e090 100644
--- a/src/client/batch.ml
+++ b/src/client/batch.ml
@@ -1,6 +1,7 @@
 type 'a t = {
   mutable size: int;
-  mutable q: 'a list list;
+  mutable q: 'a list;
+      (* The queue is a FIFO represented as a list in reverse order *)
   batch: int; (* Minimum size to batch before popping *)
   high_watermark: int;
   timeout: Mtime.span option;
@@ -42,16 +43,23 @@ let ready_to_pop ~force ~now self =
 
 let pop_if_ready ?(force = false) ~now (self : _ t) : _ list option =
   if ready_to_pop ~force ~now self then (
-    let l = self.q in
+    assert (self.q <> []);
+    let batch =
+      (* Reverse the list to retrieve the FIFO order. *)
+      List.rev self.q
+    in
     self.q <- [];
     self.size <- 0;
-    assert (l <> []);
-    let ls = List.fold_left (fun acc l -> List.rev_append l acc) [] l in
-    Some ls
+    Some batch
   ) else
     None
 
-let push (self : _ t) x : [ `Dropped | `Ok ] =
+(* Helper so we can count new elements and prepend them onto the existing [q] in
+   one pass. *)
+let append_with_count ~(elems : 'a list) ~(q : 'a list) : int * 'a list =
+  elems |> List.fold_left (fun (count, q') x -> succ count, x :: q') (0, q)
+
+let push (self : _ t) elems : [ `Dropped | `Ok ] =
   if self.size >= self.high_watermark then
     (* drop this to prevent queue from growing too fast *)
     `Dropped
@@ -60,8 +68,9 @@ let push (self : _ t) x : [ `Dropped | `Ok ] =
       (* current batch starts now *)
       self.start <- Mtime_clock.now ();
 
+    let count, q' = append_with_count ~elems ~q:self.q in
     (* add to queue *)
-    self.size <- 1 + self.size;
-    self.q <- x :: self.q;
+    self.size <- self.size + count;
+    self.q <- q';
     `Ok
   )