diff --git a/src/index.ml b/src/index.ml
index 3183b579..eb746b3d 100644
--- a/src/index.ml
+++ b/src/index.ml
@@ -303,7 +303,7 @@ struct
         hook `Before_offset_read;
         let h = IO.Header.get log.io in
         hook `After_offset_read;
-        if t.generation <> h.generation then (
+        if t.generation < h.generation then (
           (* If the generation has changed, then we need to reload both the
              [index] and the [log]. The new generation is the one on disk. *)
           Log.debug (fun l ->
@@ -323,13 +323,14 @@ struct
               l "[%s] new entries detected, reading log from disk"
                 (Filename.basename t.root));
           sync_log_entries ~min:log_offset log)
-        else
+        else if log_offset = h.offset then
           (* Here the disk offset should be equal to the known one. A smaller
              offset should not be possible, because that would mean a [clear] or
              [merge] occurred, which should have changed the generation. *)
           (* TODO: Handle the "impossible" case differently? *)
           Log.debug (fun l ->
               l "[%s] no changes detected" (Filename.basename t.root))
+        else assert false
 
   (** {1 Find and Mem}*)
 
diff --git a/test/unix/concurrent.ml b/test/unix/concurrent.ml
new file mode 100644
index 00000000..cebaec5f
--- /dev/null
+++ b/test/unix/concurrent.ml
@@ -0,0 +1,154 @@
+module Hook = Index.Private.Hook
+open Common
+
+let ( // ) = Filename.concat
+let root = "_tests" // "unix.concurrent"
+let src = Logs.Src.create "tests.unix.concurrent" ~doc:"Tests"
+
+module Log = (val Logs.src_log src : Logs.LOG)
+
+module Context = Common.Make_context (struct
+  let root = root
+end)
+
+(* Helpers for Unix pipe *)
+let write input =
+  let m = Bytes.of_string (string_of_int (Unix.getpid ())) in
+  let n = Unix.write input m 0 (Bytes.length m) in
+  assert (n = Bytes.length m)
+
+let read output =
+  let buff = Bytes.create 5 in
+  match Unix.read output buff 0 5 with
+  | 0 -> Alcotest.fail "Something wrong when reading from the pipe"
+  | n -> int_of_string (Bytes.to_string (Bytes.sub buff 0 n))
+
+let ignore_pid (_ : int) = ()
+
+let wait pid =
+  let pid', status = Unix.waitpid [ Unix.WUNTRACED ] pid in
+  if pid <> pid' then
+    Alcotest.failf "I'm %d, expecting child %d, but got %d instead"
+      (Unix.getpid ()) pid pid';
+  match status with
+  | Unix.WEXITED 0 -> Log.debug (fun l -> l "Child %d finished work" pid)
+  | _ -> Alcotest.failf "Child %d died unexpectedly" pid
+
+let lsof () =
+  let name = "/tmp/" in
+  let pid = string_of_int (Unix.getpid ()) in
+  let fd_file = name ^ "tmp_" ^ pid in
+  let lsof_command = "lsof -a -s -p " ^ pid ^ " >> " ^ fd_file in
+  match Unix.system lsof_command with
+  | Unix.WEXITED 0 -> ()
+  | Unix.WEXITED _ ->
+      failwith "failing `lsof` command. Is `lsof` installed on your system?"
+  | Unix.WSIGNALED _ | Unix.WSTOPPED _ ->
+      failwith "`lsof` command was interrupted"
+
+module WriteBatch = struct
+  let nb_workers = 1
+  let nb_batch_writes = 1000
+  let batch_size = 5
+
+  let populate_array () =
+    Array.init (batch_size * nb_batch_writes) (fun _ ->
+        let k = Key.v () in
+        let v = Value.v () in
+        (k, v))
+
+  let test_find_present ~ro t arr batch =
+    let start_ = (batch - 1) * batch_size in
+    let end_ = (batch_size * batch) - 1 in
+    Fmt.epr "%b read %d from %d to %d\n%!" ro batch start_ end_;
+    for i = start_ to end_ do
+      let k, v = arr.(i) in
+      let v' = Index.find t k in
+      if not (v = v') then raise Not_found
+    done
+
+  let test_find_absent ~ro t arr batch =
+    let start_ = (batch - 1) * batch_size in
+    let end_ = (batch_size * batch) - 1 in
+    Fmt.epr "%b read absent %d from %d to %d\n%!" ro batch start_ end_;
+    for i = start_ to end_ do
+      let k, _ = arr.(i) in
+      match Index.find t k with
+      | exception Not_found -> ()
+      | _ -> Alcotest.failf "Found %s key after clear " k
+    done
+
+  let add_values t arr batch =
+    Index.clear t;
+    let start_ = (batch - 1) * batch_size in
+    let end_ = (batch_size * batch) - 1 in
+    Fmt.epr "add values %d to %d\n%!" start_ end_;
+    for i = start_ to end_ do
+      let k, v = arr.(i) in
+      Index.replace t k v
+    done;
+    Index.flush t
+
+  let worker input_write output_read name arr =
+    let r = Index.v ~fresh:false ~log_size:4 ~readonly:true name in
+    for i = 1 to nb_batch_writes do
+      write input_write;
+      ignore (read output_read);
+      Index.sync r;
+      test_find_present ~ro:true r arr i;
+      Log.debug (fun l -> l "RO read by %d" (Unix.getpid ()))
+    done;
+    write input_write;
+    ignore (read output_read);
+    Index.sync r;
+    test_find_absent ~ro:true r arr nb_batch_writes
+
+  let concurrent_reads () =
+    let output_write, input_write = Unix.pipe ()
+    and output_read, input_read = Unix.pipe () in
+    let root = Context.fresh_name "empty_index" in
+    let arr = populate_array () in
+    match Unix.fork () with
+    | 0 ->
+        Log.debug (fun l -> l "I'm %d" (Unix.getpid ()));
+        worker input_write output_read root arr;
+        exit 0
+    | pid ->
+        Log.debug (fun l ->
+            l "I'm main process %d, created %d" (Unix.getpid ()) pid);
+        let rw = Index.v ~fresh:true ~log_size:4 root in
+        for i = 1 to nb_batch_writes do
+          Log.debug (fun l -> l "Starting batch nb %d" i);
+          if i mod 100 = 0 then lsof ();
+          for _ = 0 to nb_workers - 1 do
+            let pid = read output_write in
+            Log.debug (fun l -> l "Ack from %d" pid)
+          done;
+          add_values rw arr i;
+          for _ = 0 to nb_workers - 1 do
+            write input_read
+          done;
+          test_find_present ~ro:false rw arr i;
+          Log.debug (fun l -> l "Write from rw index")
+        done;
+        for _ = 0 to nb_workers - 1 do
+          let pid = read output_write in
+          Log.debug (fun l -> l "Ack from %d" pid)
+        done;
+        Index.clear rw;
+        for _ = 0 to nb_workers - 1 do
+          write input_read
+        done;
+        wait pid;
+        Unix.close input_write;
+        Unix.close output_write;
+        Unix.close input_read;
+        Unix.close output_read
+
+  let check_os () = if Sys.os_type = "Win32" then () else concurrent_reads ()
+  let tests = [ ("concurrent reads and writes", `Quick, check_os) ]
+end
+
+let () =
+  (* Common.report (); *)
+  Alcotest.run ~verbose:true "concurrent" [ ("write batch", WriteBatch.tests) ]
diff --git a/test/unix/dune b/test/unix/dune
index c850fd8d..b9dd232e 100644
--- a/test/unix/dune
+++ b/test/unix/dune
@@ -1,5 +1,5 @@
 (tests
- (names main force_merge io_array)
+ (names main force_merge io_array concurrent)
  (package index)
  (libraries index index.unix alcotest fmt logs logs.fmt re stdlib-shims
    threads.posix repr semaphore-compat optint))
diff --git a/test/unix/main.ml b/test/unix/main.ml
index 0368ade0..00f75031 100644
--- a/test/unix/main.ml
+++ b/test/unix/main.ml
@@ -592,6 +592,54 @@ module Readonly = struct
     Alcotest.(check int) "reloadings of log async per merge" 1 !reload_log_async;
     Index.await t |> check_completed
 
+  let race_log_async () =
+    let* Context.{ rw; clone; _ } = Context.with_empty_index () in
+    let ro = clone ~readonly:true () in
+    let merge = Semaphore.make false in
+    let sync = Semaphore.make false in
+    let merge2 = Semaphore.make false in
+    let merge_hook1 =
+      I.Private.Hook.v @@ function
+      | `Before ->
+          Semaphore.acquire merge;
+          Semaphore.release sync
+      | `After_clear -> Index.sync ro
+      | _ -> ()
+    in
+    let merge_hook2 =
+      I.Private.Hook.v @@ function
+      | `Before ->
+          Semaphore.acquire merge2;
+          Semaphore.acquire merge
+      | _ -> ()
+    in
+    let k1, v1 = (Key.v (), Value.v ()) in
+    let k2, v2 = (Key.v (), Value.v ()) in
+    let k3, v3 = (Key.v (), Value.v ()) in
+    let k4, v4 = (Key.v (), Value.v ()) in
+    Index.replace rw k1 v1;
+    Index.flush rw;
+    let t = Index.try_merge_aux ~force:true ~hook:merge_hook1 rw in
+    Semaphore.release merge;
+    Log.debug (fun l -> l "read log async");
+    Index.replace rw k2 v2;
+    Index.flush rw;
+    Index.sync ro;
+    Index.check_binding ro k2 v2;
+    Semaphore.acquire sync;
+    Index.await t |> check_completed;
+    Index.replace rw k3 v3;
+    Index.flush rw;
+    let t = Index.try_merge_aux ~force:true ~hook:merge_hook2 rw in
+    Semaphore.release merge2;
+    Log.debug (fun l -> l "XXX read log async after second merge");
+    Index.replace rw k4 v4;
+    Index.flush rw;
+    Index.sync ro;
+    Index.check_binding ro k4 v4;
+    Semaphore.release merge;
+    Index.await t |> check_completed
+
   let tests =
     [
       ("add", `Quick, readonly);
@@ -618,6 +666,7 @@ module Readonly = struct
         `Quick,
         readonly_sync_and_merge_clear );
       ("reload log and log async", `Quick, reload_log_async);
+      ("race log async", `Quick, race_log_async);
     ]
 end
 
@@ -899,6 +948,35 @@ module Throttle = struct
     ]
 end
 
+module BatchReads = struct
+  let add_values ?(batch_size = 10) t tbl =
+    let rec loop i =
+      if i = 0 then Index.flush t
+      else
+        let k = Key.v () in
+        let v = Value.v () in
+        Index.replace t k v;
+        Hashtbl.replace tbl k v;
+        loop (i - 1)
+    in
+    loop batch_size
+
+  let readonly_reads_rw_writes () =
+    let nb_batch_writes = 3 in
+    let* Context.{ rw; tbl; clone; _ } = Context.with_full_index () in
+    let ro = clone ~readonly:true () in
+    check_equivalence ro tbl;
+
+    for _i = 0 to nb_batch_writes do
+      add_values rw tbl;
+      (* check_equivalence rw tbl; *)
+      Index.sync ro;
+      check_equivalence ro tbl
+    done
+
+  let tests = [ ("reads and writes", `Quick, readonly_reads_rw_writes) ]
+end
+
 let () =
   Common.report ();
   Alcotest.run "index.unix"
@@ -912,4 +990,5 @@ let () =
       ("filter", Filter.tests);
       ("flush_callback", Flush_callback.tests);
       ("throttle", Throttle.tests);
+      ("batch", BatchReads.tests);
     ]