diff --git a/core/src/render/ascii.rs b/core/src/render/ascii.rs
index 9d2f2f4..83c353e 100644
--- a/core/src/render/ascii.rs
+++ b/core/src/render/ascii.rs
@@ -12,12 +12,11 @@ pub fn render_ascii(qr: &QrCode, invert: bool) -> String {
     let mut result = String::new();
     for y in 0..total {
         for x in 0..total {
-            let mx = x.saturating_sub(margin);
-            let my = y.saturating_sub(margin);
-            let is_dark = if mx < size && my < size {
-                qr.modules()[my][mx]
+            let in_qr = x >= margin && x < margin + size && y >= margin && y < margin + size;
+            let is_dark = if in_qr {
+                qr.modules()[y - margin][x - margin]
             } else {
-                false
+                false // 静区始终为亮色
             };
             result.push_str(if is_dark { dark_char } else { light_char });
         }