diff --git a/fxbarcode/common/BC_CommonByteMatrix.cpp b/fxbarcode/common/BC_CommonByteMatrix.cpp
index d299d4b..baba324 100644
--- a/fxbarcode/common/BC_CommonByteMatrix.cpp
+++ b/fxbarcode/common/BC_CommonByteMatrix.cpp
@@ -24,28 +24,30 @@
 #include <algorithm>
 #include <iterator>
 #include "core/fxcrt/stl_util.h"
+#include "third_party/base/check_op.h"
 
-CBC_CommonByteMatrix::CBC_CommonByteMatrix(int32_t width, int32_t height)
+CBC_CommonByteMatrix::CBC_CommonByteMatrix(size_t width, size_t height)
     : m_width(width), m_height(height) {
-  m_bytes =
-      fxcrt::Vector2D<uint8_t, FxAllocAllocator<uint8_t>>(m_height, m_width);
-  clear(0xff);
+  static constexpr size_t kMaxBytes = 256 * 1024 * 1024;  // 256 MB.
+  CHECK_LT(width, kMaxBytes / height);
+  m_bytes = fxcrt::Vector2D<uint8_t, FxAllocAllocator<uint8_t>>(height, width);
+  Fill(0xff);
 }
 
 CBC_CommonByteMatrix::~CBC_CommonByteMatrix() = default;
 
-uint8_t CBC_CommonByteMatrix::Get(int32_t x, int32_t y) const {
-  return m_bytes[y * m_width + x];
+uint8_t CBC_CommonByteMatrix::Get(size_t x, size_t y) const {
+  const size_t offset = y * m_width + x;
+  CHECK_LT(offset, m_bytes.size());
+  return m_bytes[offset];
 }
 
-void CBC_CommonByteMatrix::Set(int32_t x, int32_t y, int32_t value) {
-  m_bytes[y * m_width + x] = (uint8_t)value;
+void CBC_CommonByteMatrix::Set(size_t x, size_t y, uint8_t value) {
+  const size_t offset = y * m_width + x;
+  CHECK_LT(offset, m_bytes.size());
+  m_bytes[offset] = value;
 }
 
-void CBC_CommonByteMatrix::Set(int32_t x, int32_t y, uint8_t value) {
-  m_bytes[y * m_width + x] = value;
-}
-
-void CBC_CommonByteMatrix::clear(uint8_t value) {
+void CBC_CommonByteMatrix::Fill(uint8_t value) {
   std::fill(std::begin(m_bytes), std::end(m_bytes), value);
 }
diff --git a/fxbarcode/common/BC_CommonByteMatrix.h b/fxbarcode/common/BC_CommonByteMatrix.h
index 0b95f73..970acf8 100644
--- a/fxbarcode/common/BC_CommonByteMatrix.h
+++ b/fxbarcode/common/BC_CommonByteMatrix.h
@@ -16,21 +16,20 @@
 
 class CBC_CommonByteMatrix final {
  public:
-  CBC_CommonByteMatrix(int32_t width, int32_t height);
+  CBC_CommonByteMatrix(size_t width, size_t height);
   ~CBC_CommonByteMatrix();
 
-  int32_t GetWidth() const { return m_width; }
-  int32_t GetHeight() const { return m_height; }
+  size_t GetWidth() const { return m_width; }
+  size_t GetHeight() const { return m_height; }
   pdfium::span<const uint8_t> GetArray() const { return m_bytes; }
-  uint8_t Get(int32_t x, int32_t y) const;
 
-  void Set(int32_t x, int32_t y, int32_t value);
-  void Set(int32_t x, int32_t y, uint8_t value);
-  void clear(uint8_t value);
+  uint8_t Get(size_t x, size_t y) const;
+  void Set(size_t x, size_t y, uint8_t value);
+  void Fill(uint8_t value);
 
  private:
-  int32_t m_width;
-  int32_t m_height;
+  const size_t m_width;
+  const size_t m_height;
   std::vector<uint8_t, FxAllocAllocator<uint8_t>> m_bytes;
 };
 
diff --git a/fxbarcode/qrcode/BC_QRCoder.cpp b/fxbarcode/qrcode/BC_QRCoder.cpp
index 46f80fc..02ab3e4 100644
--- a/fxbarcode/qrcode/BC_QRCoder.cpp
+++ b/fxbarcode/qrcode/BC_QRCoder.cpp
@@ -26,6 +26,7 @@
 #include "fxbarcode/qrcode/BC_QRCoder.h"
 #include "fxbarcode/qrcode/BC_QRCoderErrorCorrectionLevel.h"
 #include "fxbarcode/qrcode/BC_QRCoderMode.h"
+#include "third_party/base/numerics/safe_conversions.h"
 
 CBC_QRCoder::CBC_QRCoder() = default;
 
@@ -69,7 +70,8 @@
          m_numECBytes != -1 && m_numRSBlocks != -1 &&
          IsValidMaskPattern(m_maskPattern) &&
          m_numTotalBytes == m_numDataBytes + m_numECBytes && m_matrix &&
-         m_matrixWidth == m_matrix->GetWidth() &&
+         m_matrixWidth ==
+             pdfium::base::checked_cast<int32_t>(m_matrix->GetWidth()) &&
          m_matrix->GetWidth() == m_matrix->GetHeight();
 }
 
diff --git a/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp b/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp
index 11008d9..23d76f9 100644
--- a/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp
+++ b/fxbarcode/qrcode/BC_QRCoderMatrixUtil.cpp
@@ -106,7 +106,7 @@
     if (x == 6)
       x -= 1;
 
-    while (y >= 0 && y < matrix->GetHeight()) {
+    while (y >= 0 && y < static_cast<int32_t>(matrix->GetHeight())) {
       if (y == 6) {
         y += direction;
         continue;
@@ -215,8 +215,8 @@
 }
 
 bool EmbedTimingPatterns(CBC_CommonByteMatrix* matrix) {
-  for (int32_t i = 8; i < matrix->GetWidth() - 8; i++) {
-    int32_t bit = (i + 1) % 2;
+  for (size_t i = 8; i + 8 < matrix->GetWidth(); i++) {
+    const uint8_t bit = static_cast<uint8_t>((i + 1) % 2);
     if (!IsValidValue(matrix->Get(i, 6)))
       return false;
 
@@ -378,7 +378,7 @@
   if (!dataBits || !matrix)
     return false;
 
-  matrix->clear(0xff);
+  matrix->Fill(0xff);
 
   if (!EmbedBasicPatterns(version, matrix))
     return false;