diff --git a/native_bridge/src/RenderFxJob.cpp b/native_bridge/src/RenderFxJob.cpp
index 82faa88..dcf9092 100644
--- a/native_bridge/src/RenderFxJob.cpp
+++ b/native_bridge/src/RenderFxJob.cpp
@@ -881,7 +881,7 @@ int run_render_fx_job(const std::string& jobPath, const std::string& inPath,
     for (uint64_t pos = 0; pos < in.L.size(); pos += chunk) {
         const uint32_t n = (uint32_t)std::min<uint64_t>(chunk, in.L.size() - pos);
         writeFrames(wav, in.L.data() + pos, in.R.data() + pos, n);
-        dataBytes += (uint64_t)n * 4;
+        dataBytes += (uint64_t)n * 8;  // stereo float32: 2ch * 4B
     }
     finishWav(wav, dataBytes);
     wav.close();
diff --git a/native_bridge/src/RenderJob.cpp b/native_bridge/src/RenderJob.cpp
index 65c8aee..9b8dd84 100644
--- a/native_bridge/src/RenderJob.cpp
+++ b/native_bridge/src/RenderJob.cpp
@@ -388,7 +388,7 @@ int run_render_job(const std::string& jobPath, const std::string& outPath) {
         const uint32_t n = (uint32_t)(to - from);
         mgr.renderAll(L.data(), R.data(), n);
         writeFrames(wav, L.data(), R.data(), n);
-        dataBytes += (uint64_t)n * 4;
+        dataBytes += (uint64_t)n * 8;  // stereo float32: 2ch * 4B
     };
     while (pos < totalNeeded) {
         const uint64_t chunkEnd = std::min(pos + chunk, (uint64_t)totalNeeded);
diff --git a/tests/test_lossless_compliance.py b/tests/test_lossless_compliance.py
index c2b8011..00d643f 100644
--- a/tests/test_lossless_compliance.py
+++ b/tests/test_lossless_compliance.py
@@ -43,6 +43,8 @@ def wav_format_info(path):
     with open(path, "rb") as f:
         b = f.read(44)
     assert b[:4] == b"RIFF" and b[8:12] == b"WAVE", "not RIFF/WAVE"
+    data_size = struct.unpack_from("<I", b, 40)[0]
+    assert os.path.getsize(path) == 44 + data_size, "data chunk size mismatch"
     return {
         "fmt_tag": struct.unpack_from("<H", b, 20)[0],
         "channels": struct.unpack_from("<H", b, 22)[0],