diff --git a/dune-project b/dune-project
index cd0328d3..0582156a 100644
--- a/dune-project
+++ b/dune-project
@@ -45,6 +45,6 @@
   (synopsis "Use eio for tiny_httpd")
   (depends
     (tiny_httpd (= :version))
-    eio
+    (eio (and (>= 1.0) (< 2.0)))
     (logs :with-test)
     (odoc :with-doc)))
diff --git a/tiny_httpd_eio.opam b/tiny_httpd_eio.opam
index cdc15a35..15b2a090 100644
--- a/tiny_httpd_eio.opam
+++ b/tiny_httpd_eio.opam
@@ -10,7 +10,7 @@ bug-reports: "https://github.com/c-cube/tiny_httpd/issues"
 depends: [
   "dune" {>= "3.2"}
   "tiny_httpd" {= version}
-  "eio"
+  "eio" {>= "1.0" & < "2.0"}
   "logs" {with-test}
   "odoc" {with-doc}
 ]