diff --git a/packages/yocaml/yocaml.1.0.0/opam b/packages/yocaml/yocaml.1.0.0/opam
index b3165a0be66..69a0acda9d1 100644
--- a/packages/yocaml/yocaml.1.0.0/opam
+++ b/packages/yocaml/yocaml.1.0.0/opam
@@ -23,6 +23,9 @@ depends: [
   "alcotest" {with-test}
   "preface" { >= "1.0.0"}
 ]
+conflicts: [
+  "base-effects"
+]
 url {
   src:
     "https://github.com/xhtmlboi/yocaml/releases/download/v1.0.0/yocaml-1.0.0.tbz"