diff --git a/src/lib_storage/context.ml b/src/lib_storage/context.ml
index c166337d4b857c8eba8a7ea18e6abb8787852aa4..d5f5c3a8c5931d71b91c15d5979c972f12926892 100644
--- a/src/lib_storage/context.ml
+++ b/src/lib_storage/context.ml
@@ -140,14 +140,12 @@ module Node = struct
 
     type entry = {kind : kind; name : M.step; node : Hash.t}
 
-    let s = Irmin.Type.(string_of `Int64)
+    (* Irmin 1.4 uses int8 to store filename lengths.
 
-    let pre_hash_v = Irmin.Type.(unstage (pre_hash s))
-
-    (* Irmin 1.4 uses int64 to store string lengths *)
-    let step_t =
-      let pre_hash = Irmin.Type.(stage @@ fun x -> pre_hash_v x) in
-      Irmin.Type.like M.step_t ~pre_hash
+       Irmin 2 use a variable-size encoding for strings; this is using int8
+       for strings of size stricly less than 128 (e.g. 2^7) which happen to
+       be the case for all filenames ever produced by Irmin 1.4. *)
+    let step_t = Irmin.Type.string
 
     let metadata_t =
       let some = "\255\000\000\000\000\000\000\000" in
diff --git a/src/lib_storage/test/assert.ml b/src/lib_storage/test/assert.ml
index f644002686b4c2aec339cee0de9a5a0868a98c79..0d05047a48c2eee4e9a5ddbf9c9ed291746f82e1 100644
--- a/src/lib_storage/test/assert.ml
+++ b/src/lib_storage/test/assert.ml
@@ -100,6 +100,9 @@ let equal_key_dir_list ?msg l1 l2 =
     l1
     l2
 
+let equal_context_hash ?msg l1 l2 =
+  equal ?msg ~eq:Context_hash.( = ) ~prn:Context_hash.to_b58check l1 l2
+
 let equal_context_hash_list ?msg l1 l2 =
   let pr_persist hash = Printf.sprintf "[%s]" @@ Context_hash.to_string hash in
   make_equal_list ?msg Context_hash.( = ) pr_persist l1 l2
diff --git a/src/lib_storage/test/test_context.ml b/src/lib_storage/test/test_context.ml
index 5643e5ee1530a90e27f33fce55fe0a7df51247c6..1594c0b68e8097d3e8600245ddd66351999a37e5 100644
--- a/src/lib_storage/test/test_context.ml
+++ b/src/lib_storage/test/test_context.ml
@@ -457,6 +457,46 @@ let test_raw {idx; genesis; _} =
       Assert.equal_raw_tree ~msg:__LOC__ e raw ;
       Lwt.return ()
 
+let string n = String.make n 'a'
+
+let test_encoding {idx; genesis; _} =
+  checkout idx genesis
+  >>= function
+  | None ->
+      Assert.fail_msg "checkout genesis_block"
+  | Some ctxt ->
+      let foo1 = Bytes.of_string "foo1" in
+      let foo2 = Bytes.of_string "foo2" in
+      add ctxt ["a"; string 7] foo1
+      >>= fun ctxt ->
+      add ctxt ["a"; string 8] foo2
+      >>= fun ctxt ->
+      add ctxt [string 16] foo2
+      >>= fun ctxt ->
+      add ctxt [string 32] foo2
+      >>= fun ctxt ->
+      add ctxt [string 64] foo2
+      >>= fun ctxt ->
+      add ctxt [string 127] foo2
+      >>= fun ctxt ->
+      commit ctxt
+      >>= fun h ->
+      Assert.equal_context_hash
+        ~msg:__LOC__
+        (Context_hash.of_b58check_exn
+           "CoWJsL2ehZ39seTr8inBCJb5tVjW8KGNweJ5cvuVq51mAASrRmim")
+        h ;
+      add ctxt [string 255] foo2
+      >>= fun ctxt ->
+      commit ctxt
+      >>= fun h ->
+      Assert.equal_context_hash
+        ~msg:__LOC__
+        (Context_hash.of_b58check_exn
+           "CoVexcEHMXmSA2k42aNc5MCDtVJFRs3CC6vcQWYwFoj7EFsBPw1c")
+        h ;
+      Lwt.return ()
+
 let test_dump {idx; block3b; _} =
   Lwt_utils_unix.with_tempdir "tezos_test_" (fun base_dir2 ->
       let dumpfile = base_dir2 // "dump" in
@@ -534,7 +574,8 @@ let tests : (string * (t -> unit Lwt.t)) list =
     ("fold", test_fold);
     ("trees", test_trees);
     ("raw", test_raw);
-    ("dump", test_dump) ]
+    ("dump", test_dump);
+    ("encoding", test_encoding) ]
 
 let tests =
   List.map