diff --git a/ca-certs.opam b/ca-certs.opam
index 0e68af7..531c85d 100644
--- a/ca-certs.opam
+++ b/ca-certs.opam
@@ -24,6 +24,7 @@ depends: [
   "mirage-crypto" {>= "1.0.0"}
   "x509" {>= "1.0.0"}
   "ocaml" {>= "4.08.0"}
+  "ohex" {>= "0.2.0"}
   "alcotest" {with-test}
   "fmt" {with-test & >= "0.8.7"}
 ]
diff --git a/dune-project b/dune-project
index 1a11dc4..f37743e 100644
--- a/dune-project
+++ b/dune-project
@@ -16,6 +16,7 @@
   (mirage-crypto (>= 1.0.0))
   (x509 (>= 1.0.0))
   (ocaml (>= 4.08.0))
+  (ohex (>= 0.2.0))
   (alcotest :with-test)
   (fmt (and :with-test (>= 0.8.7))))
  (conflicts (result (< 1.5)))