diff --git a/opam/opam b/opam/opam
index aabcdf4efa9bdfe37eef904ae2e582a174d9b94b..3390d683f7207a54053cd619c662bd6fc71d4c7c 100644
--- a/opam/opam
+++ b/opam/opam
@@ -16,7 +16,7 @@ Thanks to this approach, Frama-C provides sophisticated tools, including:
 These plug-ins communicate between each other via the Frama-C API
 and via ACSL (ANSI/ISO C Specification Language) properties.
 """
-version: "21.1"
+version: "21.1+THS-1"
 maintainer: "francois.bobot@cea.fr"
 authors: [
   "Michele Alberti"