diff --git a/num/lib/dune b/num/lib/dune
index 5247be1..9431a5f 100644
--- a/num/lib/dune
+++ b/num/lib/dune
@@ -2,4 +2,5 @@
  (name sexplib_num)
  (public_name sexplib.num)
  (libraries num sexplib)
- (preprocess no_preprocessing))
+ (preprocess no_preprocessing)
+ (optional))
diff --git a/sexplib.opam b/sexplib.opam
index 35f63dd..db6149c 100644
--- a/sexplib.opam
+++ b/sexplib.opam
@@ -14,6 +14,8 @@ depends: [
   "parsexp"
   "sexplib0"
   "dune"     {>= "3.11.0"}
+]
+depopts: [
   "num"
 ]
 available: arch != "arm32" & arch != "x86_32"