diff --git a/compat/fsmonitor/fsm-settings-win32.c b/compat/fsmonitor/fsm-settings-win32.c
index b6f6744494..0f2aa321f6 100644
--- a/compat/fsmonitor/fsm-settings-win32.c
+++ b/compat/fsmonitor/fsm-settings-win32.c
@@ -25,7 +25,7 @@ static enum fsmonitor_reason check_vfs4git(struct repository *r)
 	return FSMONITOR_REASON_OK;
 }
 
-enum fsmonitor_reason fsm_os__incompatible(struct repository *r, int ipc)
+enum fsmonitor_reason fsm_os__incompatible(struct repository *r, int ipc UNUSED)
 {
 	enum fsmonitor_reason reason;