diff --git a/mirage-crypto-ec.opam b/mirage-crypto-ec.opam
index 6efd150e..58379a08 100644
--- a/mirage-crypto-ec.opam
+++ b/mirage-crypto-ec.opam
@@ -38,6 +38,7 @@ depends: [
   "yojson" {with-test & >= "1.6.0"}
   "asn1-combinators" {with-test & >= "0.3.1"}
   "ohex" {with-test & >= "0.2.0"}
+  "ounit2" {with-test}
 ]
 conflicts: [
   "ocaml-freestanding"