diff --git a/bin/admin.ml b/bin/admin.ml
index dd562e2..28795ad 100644
--- a/bin/admin.ml
+++ b/bin/admin.ml
@@ -64,9 +64,9 @@ let show () cap_path terse pool worker =
 
 let check_exit_status = function
   | Unix.WEXITED 0 -> ()
-  | Unix.WEXITED x -> Fmt.failwith "Sub-process failed with exit code %d" x
-  | Unix.WSIGNALED x -> Fmt.failwith "Sub-process failed with signal %d" x
-  | Unix.WSTOPPED x -> Fmt.failwith "Sub-process stopped with signal %d" x
+  | Unix.WEXITED x -> Fmt.failwith "Sub-process failed with exit code %a" Logging.pp_exit_status x
+  | Unix.WSIGNALED x -> Fmt.failwith "Sub-process failed with signal %a" Fmt.Dump.signal x
+  | Unix.WSTOPPED x -> Fmt.failwith "Sub-process stopped with signal %a" Fmt.Dump.signal x
 
 let exec () cap_path pool command =
   run cap_path @@ fun admin_service ->
diff --git a/bin/logging.ml b/bin/logging.ml
index 8eaa12d..34ae858 100644
--- a/bin/logging.ml
+++ b/bin/logging.ml
@@ -1,3 +1,9 @@
+let pp_exit_status f n =
+  if Sys.win32 && n < 0 then
+    Fmt.pf f "0x%08lx" (Int32.of_int n)
+  else
+    Fmt.int f n
+
 let pp_timestamp f x =
   let open Unix in
   let tm = localtime x in
diff --git a/bin/worker.ml b/bin/worker.ml
index c5b5752..f78cda7 100644
--- a/bin/worker.ml
+++ b/bin/worker.ml
@@ -14,9 +14,9 @@ let or_die = function
 
 let check_exit_status = function
   | Unix.WEXITED 0 -> ()
-  | Unix.WEXITED x -> Fmt.failwith "Sub-process failed with exit code %d" x
-  | Unix.WSIGNALED x -> Fmt.failwith "Sub-process failed with signal %d" x
-  | Unix.WSTOPPED x -> Fmt.failwith "Sub-process stopped with signal %d" x
+  | Unix.WEXITED x -> Fmt.failwith "Sub-process failed with exit code %a" Logging.pp_exit_status x
+  | Unix.WSIGNALED x -> Fmt.failwith "Sub-process failed with signal %a" Fmt.Dump.signal x
+  | Unix.WSTOPPED x -> Fmt.failwith "Sub-process stopped with signal %a" Fmt.Dump.signal x
 
 module Self_update = struct
   let service = "builder_agent"
diff --git a/worker/process.ml b/worker/process.ml
index f8c0b27..5f0f5bd 100644
--- a/worker/process.ml
+++ b/worker/process.ml
@@ -41,9 +41,15 @@ let exec ~label ~log ~switch ?env ?(stdin="") ?(stderr=`FD_copy Unix.stdout) ?(i
   | Unix.WSIGNALED x -> Fmt.error_msg "%s failed with signal %a" label Fmt.Dump.signal x
   | Unix.WSTOPPED x -> Fmt.error_msg "%s stopped with signal %a" label Fmt.Dump.signal x
 
+let pp_exit_status f n =
+  if Sys.win32 && n < 0 then
+    Fmt.pf f "0x%08lx" (Int32.of_int n)
+  else
+    Fmt.int f n
+
 let check_call ~label ~log ~switch ?env ?stdin ?stderr ?is_success cmd =
   exec ~label ~log ~switch ?env ?stdin ?stderr ?is_success cmd >|= function
   | Ok () -> Ok ()
   | Error `Cancelled -> Error `Cancelled
-  | Error (`Exit_code n) -> Fmt.error_msg "%s failed with exit-code %d" label n
+  | Error (`Exit_code n) -> Fmt.error_msg "%s failed with exit-code %a" label pp_exit_status n
   | Error (`Msg _) as e -> e