diff --git a/sidekick-arith.opam b/sidekick-arith.opam
index c5dad6ab..1109d14a 100644
--- a/sidekick-arith.opam
+++ b/sidekick-arith.opam
@@ -15,7 +15,7 @@ depends: [
   "containers" { >= "3.0" & < "4.0" }
   "iter" { >= "1.0" & < "2.0" }
   "ocaml" { >= "4.03" }
-  "zarith"
+  "zarith" { >= "1.8" } # for infix ops
   "alcotest" {with-test}
   "qcheck" {with-test & >= "0.16" }
 ]