diff --git a/.ocamlformat b/.ocamlformat
index 14fd10a5..4eae7930 100644
--- a/.ocamlformat
+++ b/.ocamlformat
@@ -1,4 +1,4 @@
-version = 0.18.0
+version = 0.19.0
 profile = conventional
 break-infix = fit-or-vertical
 parse-docstrings = true
diff --git a/conduit-mirage.opam b/conduit-mirage.opam
index 087877fa..4cd85f2f 100644
--- a/conduit-mirage.opam
+++ b/conduit-mirage.opam
@@ -28,6 +28,7 @@ depends: [
   "ipaddr" {>= "3.0.0"}
   "ipaddr-sexp"
   "tcpip" {with-test}
+  "fmt" {>= "0.8.7"}
 ]
 conflicts: [
   "mirage-conduit"
diff --git a/src/conduit-lwt-unix/conduit_lwt_server.ml b/src/conduit-lwt-unix/conduit_lwt_server.ml
index 7184d56b..322137a2 100644
--- a/src/conduit-lwt-unix/conduit_lwt_server.ml
+++ b/src/conduit-lwt-unix/conduit_lwt_server.ml
@@ -99,6 +99,6 @@ let init ?(stop = fst (Lwt.wait ())) handler fd =
             Log.warn (fun f ->
                 f "Uncaught exception accepting connection: %s"
                   (Printexc.to_string ex));
-            Lwt_unix.yield () >>= loop)
+            Lwt.pause () >>= loop)
   in
   Lwt.finalize loop (fun () -> Lwt_unix.close fd)
diff --git a/src/conduit-lwt-unix/conduit_lwt_tls.dummy.ml b/src/conduit-lwt-unix/conduit_lwt_tls.dummy.ml
index a20e6905..aca0f478 100644
--- a/src/conduit-lwt-unix/conduit_lwt_tls.dummy.ml
+++ b/src/conduit-lwt-unix/conduit_lwt_tls.dummy.ml
@@ -3,7 +3,7 @@ module X509 = struct
 
   type authenticator = unit
 
-  let default_authenticator = ()
+  let default_authenticator = lazy ()
 end
 
 module Client = struct
diff --git a/src/conduit-lwt-unix/conduit_lwt_tls.dummy.mli b/src/conduit-lwt-unix/conduit_lwt_tls.dummy.mli
index bed1b289..27a3e4d0 100644
--- a/src/conduit-lwt-unix/conduit_lwt_tls.dummy.mli
+++ b/src/conduit-lwt-unix/conduit_lwt_tls.dummy.mli
@@ -22,7 +22,7 @@ module X509 : sig
 
   type authenticator = unit
 
-  val default_authenticator : authenticator
+  val default_authenticator : authenticator Lazy.t
 end
 
 module Client : sig
diff --git a/src/conduit-mirage/conduit_mirage.ml b/src/conduit-mirage/conduit_mirage.ml
index 37a55502..c81230b9 100644
--- a/src/conduit-mirage/conduit_mirage.ml
+++ b/src/conduit-mirage/conduit_mirage.ml
@@ -20,7 +20,7 @@ open Sexplib.Conv
 
 let ( >>= ) = Lwt.( >>= )
 let ( >|= ) = Lwt.( >|= )
-let fail fmt = Fmt.kstrf (fun s -> Lwt.fail (Failure s)) fmt
+let fail fmt = Fmt.kstr (fun s -> Lwt.fail (Failure s)) fmt
 let err_tcp_not_supported = fail "%s: TCP is not supported"
 let err_tls_not_supported = fail "%s: TLS is not supported"
 
diff --git a/src/conduit-mirage/dune b/src/conduit-mirage/dune
index f0e2d8cd..06b1d9e1 100644
--- a/src/conduit-mirage/dune
+++ b/src/conduit-mirage/dune
@@ -7,4 +7,5 @@
  (wrapped false)
  (libraries conduit conduit-lwt mirage-stack mirage-clock mirage-random
    mirage-time mirage-flow mirage-flow-combinators dns-client.mirage
-   ipaddr-sexp vchan tls tls-mirage xenstore.client uri.services ca-certs-nss))
+   ipaddr-sexp vchan tls tls-mirage xenstore.client uri.services ca-certs-nss
+   fmt))