diff --git a/lwt.opam b/lwt.opam
index a8b3d3972..37fe44e71 100644
--- a/lwt.opam
+++ b/lwt.opam
@@ -30,6 +30,6 @@ depends: [
 depopts: ["base-threads" "base-unix" "conf-libev"]
 dev-repo: "git+https://github.com/ocsigen/lwt.git"
 build: [
-  ["dune" "exec" "-p" name "src/unix/config/discover.exe" "--" "--save" "--use-libev" "%{conf-libev:installed}%"]
+  ["dune" "exec" "-p" name "src/unix/config/discover.exe" "--" "--save" "--use-libev" {conf-libev:installed}]
   ["dune" "build" "-p" name "-j" jobs]
 ]
diff --git a/lwt.opam.template b/lwt.opam.template
index 6ffbf088a..b3ddbf663 100644
--- a/lwt.opam.template
+++ b/lwt.opam.template
@@ -1,4 +1,4 @@
 build: [
-  ["dune" "exec" "-p" name "src/unix/config/discover.exe" "--" "--save" "--use-libev" "%{conf-libev:installed}%"]
+  ["dune" "exec" "-p" name "src/unix/config/discover.exe" "--" "--save" "--use-libev" {conf-libev:installed}]
   ["dune" "build" "-p" name "-j" jobs]
 ]