diff --git a/dune-project b/dune-project
index 75f525eb..21e3f5a2 100644
--- a/dune-project
+++ b/dune-project
@@ -38,7 +38,7 @@
   (depends
    (ocaml (>= "4.08"))
    (dune (>= "2.3"))
-   mtime
+   (mtime (>= "1.4")) ; for spans
    ; atomic ; vendored
    (opentelemetry (= :version))
    (ocaml-protoc (>= 2.1))
diff --git a/opentelemetry-client-ocurl.opam b/opentelemetry-client-ocurl.opam
index e6d4b97a..7133660b 100644
--- a/opentelemetry-client-ocurl.opam
+++ b/opentelemetry-client-ocurl.opam
@@ -10,7 +10,7 @@ bug-reports:
 depends: [
   "ocaml" {>= "4.08"}
   "dune" {>= "2.3"}
-  "mtime"
+  "mtime" {>= "1.4"}
   "opentelemetry" {= version}
   "ocaml-protoc" {>= "2.1"}
   "odoc" {with-doc}