diff --git a/device-usage/block/unikernel.ml b/device-usage/block/unikernel.ml
index f1ff3458..e25b2b77 100644
--- a/device-usage/block/unikernel.ml
+++ b/device-usage/block/unikernel.ml
@@ -45,7 +45,7 @@ module Main (Time : Mirage_time.S) (B : Mirage_block.S) = struct
 
   let alloc sector_size n =
     let rec loop = function
-      | 0 -> []
+      | n when (n<=0) -> []
       | n ->
           let page = Io_page.(to_cstruct (get 1)) in
           let phrase =
diff --git a/device-usage/console/unikernel.ml b/device-usage/console/unikernel.ml
index 3dfa4652..2a2bd2c8 100644
--- a/device-usage/console/unikernel.ml
+++ b/device-usage/console/unikernel.ml
@@ -3,7 +3,7 @@ open Lwt.Infix
 module Main (C : Mirage_console.S) (Time : Mirage_time.S) = struct
   let start c _time =
     let rec loop = function
-      | 0 -> Lwt.return_unit
+      | n when (n<=0) -> Lwt.return_unit
       | n ->
           C.log c "hello" >>= fun () ->
           Time.sleep_ns (Duration.of_sec 1) >>= fun () ->
diff --git a/tutorial/hello-key/unikernel.ml b/tutorial/hello-key/unikernel.ml
index 48232798..8254485f 100644
--- a/tutorial/hello-key/unikernel.ml
+++ b/tutorial/hello-key/unikernel.ml
@@ -5,7 +5,7 @@ module Hello (Time : Mirage_time.S) = struct
     let hello = Key_gen.hello () in
 
     let rec loop = function
-      | 0 -> Lwt.return_unit
+      | n when (n<=0) -> Lwt.return_unit
       | n ->
           Logs.info (fun f -> f "%s" hello);
           Time.sleep_ns (Duration.of_sec 1) >>= fun () -> loop (n - 1)
diff --git a/tutorial/hello/unikernel.ml b/tutorial/hello/unikernel.ml
index cb9d8848..be74a55f 100644
--- a/tutorial/hello/unikernel.ml
+++ b/tutorial/hello/unikernel.ml
@@ -3,7 +3,7 @@ open Lwt.Infix
 module Hello (Time : Mirage_time.S) = struct
   let start _time =
     let rec loop = function
-      | 0 -> Lwt.return_unit
+      | n when (n<=0) -> Lwt.return_unit
       | n ->
           Logs.info (fun f -> f "hello");
           Time.sleep_ns (Duration.of_sec 1) >>= fun () -> loop (n - 1)
diff --git a/tutorial/lwt/echo_server/unikernel.ml b/tutorial/lwt/echo_server/unikernel.ml
index a5a596a0..3183365d 100644
--- a/tutorial/lwt/echo_server/unikernel.ml
+++ b/tutorial/lwt/echo_server/unikernel.ml
@@ -13,7 +13,7 @@ struct
 
   let start c _time _r =
     let rec echo_server = function
-      | 0 -> Lwt.return ()
+      | n when (n<=0) -> Lwt.return ()
       | n ->
           read_line () >>= fun s ->
           C.log c s >>= fun () -> echo_server (n - 1)