diff --git a/git-mirage.opam b/git-mirage.opam
index d7a747dc0..9ad8e285b 100644
--- a/git-mirage.opam
+++ b/git-mirage.opam
@@ -27,7 +27,7 @@ depends: [
   "ca-certs-nss"
   "mirage-crypto"
   "ptime"
-  "x509"
+  "x509" {>= "0.16.2"}
   "cstruct"
   "tcpip" {>= "7.0.0"}
   "domain-name" {>= "0.3.0"}
diff --git a/src/git-mirage/git_mirage_http.ml b/src/git-mirage/git_mirage_http.ml
index b4bbcbba0..d04681c46 100644
--- a/src/git-mirage/git_mirage_http.ml
+++ b/src/git-mirage/git_mirage_http.ml
@@ -272,22 +272,7 @@ struct
       | Some str -> (
           match X509.Authenticator.of_string str with
           | Ok auth -> auth time
-          | Error (`Msg _) ->
-              Fmt.failwith
-                "Invalid TLS authenticator: %S\n\
-                 The format of it is:\n\
-                 - [none]: no authentication\n\
-                 - [key-fp(:<hash>?):<base64-encoded fingerprint>]: to \
-                 authenticate a peer via its key fingerprintf (hash is \
-                 optional and defaults to SHA256)\n\
-                 - [cert-fp(:<hash>?):<base64-encoded fingerprint>]: to \
-                 authenticate a peer via its certificate fingerprint (hash is \
-                 optional and defaults to SHA256)\n\
-                 - [trust-anchor(:<base64-encoded DER certificate>)+] to \
-                 authenticate a peer from a list of certificates (certificate \
-                 must be in PEM format witthout header and footer (----BEGIN \
-                 CERTIFICATE----) and without newlines).\n"
-                str)
+          | Error (`Msg msg) -> failwith msg)
     in
     let tls = Tls.Config.client ~authenticator () in
     let ctx = Mimic.add git_mirage_http_tls_config tls ctx in