diff --git a/runtimes/ocaml/runtime.ml b/runtimes/ocaml/runtime.ml
index 32875286..94dc46bf 100644
--- a/runtimes/ocaml/runtime.ml
+++ b/runtimes/ocaml/runtime.ml
@@ -13,6 +13,7 @@
    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
    License for the specific language governing permissions and limitations under
    the License. *)
+open Ppx_yojson_conv_lib.Yojson_conv.Primitives
 
 type nonrec unit = unit
 type nonrec bool = bool