diff --git a/OCanren.opam b/OCanren.opam
index 54f5da8f9..b74da02f5 100644
--- a/OCanren.opam
+++ b/OCanren.opam
@@ -33,7 +33,7 @@ depends: [
   "benchmark" {with-test}
   "ocamlformat" {with-test & >= "0.26.1" & < "0.27"}
   "ppx_inline_test"
-  "mtime" {< "2.0.0"}
+  "mtime" {>= "2.0.0"}
   "odoc" {with-doc}
 ]
 build: [
diff --git a/add_timer/install_timer.ml b/add_timer/install_timer.ml
index 6a9b73fd8..f4a3c01ce 100644
--- a/add_timer/install_timer.ml
+++ b/add_timer/install_timer.ml
@@ -9,7 +9,10 @@ module Impl : T = struct
   let elapsed = Mtime_clock.elapsed
   let abs_diff start fin =
     let span = Mtime.Span.abs_diff start fin in
-    Mtime.Span.({s = to_s span; ms = to_ms span})
+    let ns = Mtime.Span.to_float_ns span in
+    let ms = ns *. 1000000.0 in
+    let s = ms *. 1000.0 in
+    {s; ms }
 
 end
 
diff --git a/dune-project b/dune-project
index 2b2b3a285..2c15cc0b8 100644
--- a/dune-project
+++ b/dune-project
@@ -34,7 +34,7 @@
     (< 0.27)))
   ppx_inline_test
   (mtime
-   (< 2.0.0)))
+   (>= 2.0.0)))
  (authors
   "Dmitrii Boulytchev https://github.com/dboulytchev"
   "Dmitrii Kosarev https://github.com/Kakadu"