diff --git a/elpi.opam b/elpi.opam
index 4a6332d47..5a4225f44 100644
--- a/elpi.opam
+++ b/elpi.opam
@@ -25,8 +25,8 @@ depends: [
   "cmdliner" {with-test}
   "dune" {>= "2.8.0"}
   "conf-time" {with-test}
-  "atdgen" {>= "2.9.1"}
-  "atdts" {>= "2.9.1"}
+  "atdgen" {>= "2.9.1" & < "2.10.0"}
+  "atdts" {>= "2.9.1" & < "2.10.0"}
 ]
 depopts: [
   "elpi-option-legacy-parser"
diff --git a/src/runtime.ml b/src/runtime.ml
index 541d3b83f..11fd7c5f8 100644
--- a/src/runtime.ml
+++ b/src/runtime.ml
@@ -2842,7 +2842,7 @@ and alternative = {
   clauses : clause list;
   next : alternative;
 }
-let noalts : alternative = Obj.magic 0
+let noalts : alternative = Obj.magic (Sys.opaque_identity 0)
 
 (******************************************************************************
   Constraint propagation