diff --git a/src/timeout/timeout.v b/src/timeout/timeout.v
index 943685d..3f75cdf 100644
--- a/src/timeout/timeout.v
+++ b/src/timeout/timeout.v
@@ -249,7 +249,7 @@ fn handle_timeout(mut p os.Process, kill_after_ms i64, signal string, preserve_s
 	if verbose {
 		eprintln('${app_name}: sending signal ${signal} to command')
 	}
-	terminate_process(p, sig_num, !foreground)
+	terminate_process(mut &p, sig_num, !foreground)
 
 	if kill_after_ms > 0 {
 		kill_start := time.now()
@@ -263,7 +263,7 @@ fn handle_timeout(mut p os.Process, kill_after_ms i64, signal string, preserve_s
 					if verbose {
 						eprintln('${app_name}: sending signal KILL to command')
 					}
-					terminate_process(p, 9, !foreground)
+					terminate_process(mut &p, 9, !foreground)
 				}
 				return handle_process_exit(mut p, preserve_status, 124)
 			}
diff --git a/src/timeout/timeout_default.c.v b/src/timeout/timeout_default.c.v
index 48f756b..a912be6 100644
--- a/src/timeout/timeout_default.c.v
+++ b/src/timeout/timeout_default.c.v
@@ -4,7 +4,7 @@ fn setup_process_group(p os.Process, foreground bool) {
 	// Fallback
 }
 
-fn terminate_process(p os.Process, sig_num int, process_group bool) {
+fn terminate_process(mut p &os.Process, sig_num int, process_group bool) {
 	// Fallback: try to kill the process
 	p.signal_kill()
 }
diff --git a/src/timeout/timeout_nix.c.v b/src/timeout/timeout_nix.c.v
index 00f4349..5a2d001 100644
--- a/src/timeout/timeout_nix.c.v
+++ b/src/timeout/timeout_nix.c.v
@@ -12,7 +12,7 @@ fn setup_process_group(p os.Process, foreground bool) {
 	}
 }
 
-fn terminate_process(p os.Process, sig_num int, process_group bool) {
+fn terminate_process(mut p &os.Process, sig_num int, process_group bool) {
 	pid := if process_group { -p.pid } else { p.pid }
 	C.kill(pid, sig_num)
 }
diff --git a/src/timeout/timeout_windows.c.v b/src/timeout/timeout_windows.c.v
index c0c688a..a035f98 100644
--- a/src/timeout/timeout_windows.c.v
+++ b/src/timeout/timeout_windows.c.v
@@ -7,7 +7,7 @@ fn setup_process_group(p os.Process, foreground bool) {
 // A pointer, because signalling a process changes it. Passing it by value, as the
 // nix version can, made the compiler reference it for us and then reject that as
 // deprecated automatic referencing.
-fn terminate_process(p os.Process, sig_num int, process_group bool) {
+fn terminate_process(mut p &os.Process, sig_num int, process_group bool) {
 	// TERM, Windows doesn't seem to support signals like Unixes does
 	if sig_num == 15 {
 		p.signal_term()