use parents around NGX_ATOMIC_T_LEN value
diff --git a/src/os/win32/ngx_atomic.h b/src/os/win32/ngx_atomic.h
index dc761a8..fc3cb40 100644
--- a/src/os/win32/ngx_atomic.h
+++ b/src/os/win32/ngx_atomic.h
@@ -17,7 +17,7 @@
 typedef int32_t                     ngx_atomic_int_t;
 typedef uint32_t                    ngx_atomic_uint_t;
 typedef volatile ngx_atomic_uint_t  ngx_atomic_t;
-#define NGX_ATOMIC_T_LEN            sizeof("-2147483648") - 1
+#define NGX_ATOMIC_T_LEN            (sizeof("-2147483648") - 1)
 
 
 #if defined( __WATCOMC__ ) || defined( __BORLANDC__ ) || ( _MSC_VER >= 1300 )