diff --git a/cocoscreator_projects/scripts/lib/skin.mjs b/cocoscreator_projects/scripts/lib/skin.mjs
index b1698a6..7cb56a6 100644
--- a/cocoscreator_projects/scripts/lib/skin.mjs
+++ b/cocoscreator_projects/scripts/lib/skin.mjs
@@ -69,7 +69,18 @@ export function validateOverrides(frameworkUiDir, overrideDir) {
     if (needSizeCheck) {
       const a = readPngSize(join(frameworkUiDir, ...rel.split(posix.sep)));
       const b = readPngSize(join(overrideDir, ...rel.split(posix.sep)));
-      if (a && b && (a.width !== b.width || a.height !== b.height)) {
+      if (!a || !b) {
+        const side = !a ? '框架' : 'override';
+        errors.push({
+          path: rel,
+          code: 'size-unreadable',
+          message:
+            `框架 UI 图片必须是 PNG（无法读取尺寸：${side}）。` +
+            `请改用 PNG，或连 .meta 一起提供（例外通道）`,
+        });
+        continue;
+      }
+      if (a.width !== b.width || a.height !== b.height) {
         errors.push({
           path: rel,
           code: 'size-mismatch',
diff --git a/cocoscreator_projects/scripts/test/skin.test.mjs b/cocoscreator_projects/scripts/test/skin.test.mjs
index e413bae..4022e3a 100644
--- a/cocoscreator_projects/scripts/test/skin.test.mjs
+++ b/cocoscreator_projects/scripts/test/skin.test.mjs
@@ -147,13 +147,41 @@ test('图片尺寸不同但自带 meta（例外通道）→ 通过', () => {
 test('非图片资源（音效）不做尺寸校验', () => {
   const d = makeDirs();
   try {
-    writeFile(d.fw, 'audio/click.wav', 'aaaa');
-    writeFile(d.ov, 'audio/click.wav', 'bbbbbbbbbbbb');
+    // 用真实的、有效的、尺寸不同的 PNG 字节，但扩展名是 .wav
+    // 如果 isImage() 门控被删掉，因为尺寸不同会报 size-mismatch，用例失败
+    writeFile(d.fw, 'audio/click.wav', makePng(64, 64));
+    writeFile(d.ov, 'audio/click.wav', makePng(256, 256));
     const r = validateOverrides(d.fw, d.ov);
     assert.deepEqual(r.errors, []);
   } finally { cleanup(d.root); }
 });
 
+// ---- validateOverrides：尺寸不可读 ----
+test('图片尺寸无法读取（非 PNG）→ size-unreadable', () => {
+  const d = makeDirs();
+  try {
+    png(d.fw, 'atlas-hall/btn.png', 64, 64);
+    writeFile(d.ov, 'atlas-hall/btn.png', 'this is not a png but it is long enough to pass the 24-byte length check');
+    const r = validateOverrides(d.fw, d.ov);
+    assert.equal(r.errors.length, 1);
+    assert.equal(r.errors[0].code, 'size-unreadable');
+    assert.match(r.errors[0].message, /无法读取尺寸/);
+    assert.match(r.errors[0].message, /PNG/);
+    assert.equal(r.matched.length, 0);
+  } finally { cleanup(d.root); }
+});
+
+test('readPngSize 长度足够但签名不对 → 返回 null', () => {
+  const d = makeDirs();
+  try {
+    // 构造一个 24 字节以上、但 PNG 签名不对的数据
+    const buf = Buffer.alloc(30, 0x00);
+    buf.write('NOTPNG', 1, 'ascii');
+    const p = writeFile(d.fw, 'test.png', buf);
+    assert.equal(readPngSize(p), null);
+  } finally { cleanup(d.root); }
+});
+
 // ---- validateOverrides：Spine ----
 test('Spine 整套覆盖 → 通过，且贴图豁免尺寸校验', () => {
   const d = makeDirs();