diff --git a/opam b/opam
index 292905d75..29736852e 100644
--- a/opam
+++ b/opam
@@ -28,7 +28,7 @@ ocaml-version: [ >= "4.04.0" ]
 depends: [
   "ANSITerminal" {>="0.7"}
   "atdgen" {>="1.6.0"}
-  "core"
+  "core" {<"v0.9"}
   "conf-autoconf"
   "ctypes" {>="0.9.2"}
   "extlib-compat"