diff --git a/alt-ergo-lib.opam b/alt-ergo-lib.opam
index 79bfa94e1b..e9ee9c2a89 100644
--- a/alt-ergo-lib.opam
+++ b/alt-ergo-lib.opam
@@ -23,7 +23,7 @@ depends: [
   "ocplib-simplex" {>= "0.5"}
   "zarith" {>= "1.4"}
   "seq"
-  "fmt"
+  "fmt" {>= "0.9.0"}
   "stdlib-shims"
   "ppx_blob" {>= "0.7.2"}
   "camlzip" {>= "1.07"}
diff --git a/dune-project b/dune-project
index 3740e1d0ac..4df02c309b 100644
--- a/dune-project
+++ b/dune-project
@@ -83,7 +83,7 @@ See more details on http://alt-ergo.ocamlpro.com/"
   (ocplib-simplex (>= 0.5))
   (zarith (>= 1.4))
   seq
-  fmt
+  (fmt (>= 0.9.0))
   stdlib-shims
   (ppx_blob (>= 0.7.2))
   (camlzip (>= 1.07))