diff --git a/packages/why3/why3.1.8.2/opam b/packages/why3/why3.1.8.2/opam
index 7d426ad01462..87366710eb95 100644
--- a/packages/why3/why3.1.8.2/opam
+++ b/packages/why3/why3.1.8.2/opam
@@ -71,6 +71,7 @@ conflicts: [
   "why3-base"
   "ocamlgraph" {< "1.8.2"}
   "mlmpfr" {< "4.0.0"}
+  "ppxlib" {< "0.33.0"}
 ]
 
 synopsis: "Why3 environment for deductive program verification"