diff --git a/fxbarcode/datamatrix/BC_C40Encoder.cpp b/fxbarcode/datamatrix/BC_C40Encoder.cpp
index e994774..8edd9ec 100644
--- a/fxbarcode/datamatrix/BC_C40Encoder.cpp
+++ b/fxbarcode/datamatrix/BC_C40Encoder.cpp
@@ -189,8 +189,14 @@
 int32_t CBC_C40Encoder::BacktrackOneCharacter(CBC_EncoderContext* context,
                                               CFX_WideString* buffer,
                                               int32_t lastCharSize) {
+  if (context->m_pos < 1)
+    return -1;
+
   int32_t count = buffer->GetLength();
-  buffer->Delete(count - lastCharSize, count);
+  if (count < lastCharSize)
+    return -1;
+
+  buffer->Delete(count - lastCharSize, lastCharSize);
   context->m_pos--;
   wchar_t c = context->getCurrentChar();
   int32_t e = BCExceptionNO;
@@ -199,7 +205,7 @@
   if (e != BCExceptionNO)
     return -1;
 
-  assert(len > 0);
+  ASSERT(len > 0);
   context->resetSymbolInfo();
   return len;
 }
diff --git a/fxbarcode/datamatrix/BC_EncoderContext.cpp b/fxbarcode/datamatrix/BC_EncoderContext.cpp
index 40855fc..404c07d 100644
--- a/fxbarcode/datamatrix/BC_EncoderContext.cpp
+++ b/fxbarcode/datamatrix/BC_EncoderContext.cpp
@@ -34,9 +34,9 @@
   CFX_ByteString dststr;
   CBC_UtilCodingConvert::UnicodeToUTF8(msg, dststr);
   CFX_WideString sb;
-  int32_t c = dststr.GetLength();
-  for (int32_t i = 0; i < c; i++) {
-    wchar_t ch = (wchar_t)(dststr.GetAt(i) & 0xff);
+  FX_STRSIZE c = dststr.GetLength();
+  for (FX_STRSIZE i = 0; i < c; i++) {
+    wchar_t ch = static_cast<wchar_t>(dststr.GetAt(i) & 0xff);
     if (ch == '?' && dststr.GetAt(i) != '?') {
       e = BCExceptionCharactersOutsideISO88591Encoding;
     }
@@ -73,7 +73,7 @@
 void CBC_EncoderContext::writeCodeword(wchar_t codeword) {
   m_codewords += codeword;
 }
-int32_t CBC_EncoderContext::getCodewordCount() {
+FX_STRSIZE CBC_EncoderContext::getCodewordCount() {
   return m_codewords.GetLength();
 }
 void CBC_EncoderContext::signalEncoderChange(int32_t encoding) {
@@ -85,7 +85,7 @@
 bool CBC_EncoderContext::hasMoreCharacters() {
   return m_pos < getTotalMessageCharCount();
 }
-int32_t CBC_EncoderContext::getRemainingCharacters() {
+FX_STRSIZE CBC_EncoderContext::getRemainingCharacters() {
   return getTotalMessageCharCount() - m_pos;
 }
 void CBC_EncoderContext::updateSymbolInfo(int32_t& e) {
@@ -103,6 +103,6 @@
   m_allowRectangular = true;
 }
 
-int32_t CBC_EncoderContext::getTotalMessageCharCount() {
+FX_STRSIZE CBC_EncoderContext::getTotalMessageCharCount() {
   return m_msg.GetLength() - m_skipAtEnd;
 }
diff --git a/fxbarcode/datamatrix/BC_EncoderContext.h b/fxbarcode/datamatrix/BC_EncoderContext.h
index 4931501..ef4c38e 100644
--- a/fxbarcode/datamatrix/BC_EncoderContext.h
+++ b/fxbarcode/datamatrix/BC_EncoderContext.h
@@ -25,26 +25,26 @@
   wchar_t getCurrent();
   void writeCodewords(const CFX_WideString& codewords);
   void writeCodeword(wchar_t codeword);
-  int32_t getCodewordCount();
+  FX_STRSIZE getCodewordCount();
   void signalEncoderChange(int32_t encoding);
   void resetEncoderSignal();
   bool hasMoreCharacters();
-  int32_t getRemainingCharacters();
+  FX_STRSIZE getRemainingCharacters();
   void updateSymbolInfo(int32_t& e);
   void updateSymbolInfo(int32_t len, int32_t& e);
   void resetSymbolInfo();
 
   CFX_WideString m_msg;
   CFX_WideString m_codewords;
-  int32_t m_pos;
+  FX_STRSIZE m_pos;
   int32_t m_newEncoding;
   CFX_UnownedPtr<CBC_SymbolInfo> m_symbolInfo;
 
  private:
-  int32_t getTotalMessageCharCount();
+  FX_STRSIZE getTotalMessageCharCount();
 
   bool m_allowRectangular;  // Force square when false.
-  int32_t m_skipAtEnd;
+  FX_STRSIZE m_skipAtEnd;
 };
 
 #endif  // FXBARCODE_DATAMATRIX_BC_ENCODERCONTEXT_H_