diff --git a/fxbarcode/datamatrix/BC_DataMatrixWriter.cpp b/fxbarcode/datamatrix/BC_DataMatrixWriter.cpp
index db03022..5d60fbf 100644
--- a/fxbarcode/datamatrix/BC_DataMatrixWriter.cpp
+++ b/fxbarcode/datamatrix/BC_DataMatrixWriter.cpp
@@ -47,7 +47,7 @@
 
 std::unique_ptr<CBC_CommonByteMatrix> encodeLowLevel(
     CBC_DefaultPlacement* placement,
-    CBC_SymbolInfo* symbolInfo) {
+    const CBC_SymbolInfo* symbolInfo) {
   int32_t symbolWidth = symbolInfo->getSymbolDataWidth();
   ASSERT(symbolWidth);
   int32_t symbolHeight = symbolInfo->getSymbolDataHeight();
@@ -117,10 +117,12 @@
       CBC_HighLevelEncoder::EncodeHighLevel(contents, ecLevel, false);
   if (encoded.IsEmpty())
     return nullptr;
-  CBC_SymbolInfo* pSymbolInfo =
+
+  const CBC_SymbolInfo* pSymbolInfo =
       CBC_SymbolInfo::Lookup(encoded.GetLength(), false);
   if (!pSymbolInfo)
     return nullptr;
+
   WideString codewords =
       CBC_ErrorCorrection::EncodeECC200(encoded, pSymbolInfo);
   if (codewords.IsEmpty())
diff --git a/fxbarcode/datamatrix/BC_EncoderContext.h b/fxbarcode/datamatrix/BC_EncoderContext.h
index afd202d..13f0037 100644
--- a/fxbarcode/datamatrix/BC_EncoderContext.h
+++ b/fxbarcode/datamatrix/BC_EncoderContext.h
@@ -41,7 +41,7 @@
   WideString m_codewords;
   size_t m_pos = 0;
   int32_t m_newEncoding = -1;
-  UnownedPtr<CBC_SymbolInfo> m_symbolInfo;
+  UnownedPtr<const CBC_SymbolInfo> m_symbolInfo;
 
  private:
   size_t getTotalMessageCharCount();
diff --git a/fxbarcode/datamatrix/BC_SymbolInfo.cpp b/fxbarcode/datamatrix/BC_SymbolInfo.cpp
index 7ba8153..92f0f97 100644
--- a/fxbarcode/datamatrix/BC_SymbolInfo.cpp
+++ b/fxbarcode/datamatrix/BC_SymbolInfo.cpp
@@ -109,8 +109,8 @@
 
 CBC_SymbolInfo::~CBC_SymbolInfo() = default;
 
-CBC_SymbolInfo* CBC_SymbolInfo::Lookup(int32_t iDataCodewords,
-                                       bool bAllowRectangular) {
+const CBC_SymbolInfo* CBC_SymbolInfo::Lookup(int32_t iDataCodewords,
+                                             bool bAllowRectangular) {
   for (size_t i = 0; i < kSymbolsCount; i++) {
     CBC_SymbolInfo* symbol = g_symbols[i];
     if (symbol->m_rectangular && !bAllowRectangular)
diff --git a/fxbarcode/datamatrix/BC_SymbolInfo.h b/fxbarcode/datamatrix/BC_SymbolInfo.h
index 75d7149..4655cb7 100644
--- a/fxbarcode/datamatrix/BC_SymbolInfo.h
+++ b/fxbarcode/datamatrix/BC_SymbolInfo.h
@@ -22,7 +22,8 @@
   static void Initialize();
   static void Finalize();
   static void overrideSymbolSet(CBC_SymbolInfo* override);
-  static CBC_SymbolInfo* Lookup(int32_t iDataCodewords, bool bAllowRectangular);
+  static const CBC_SymbolInfo* Lookup(int32_t iDataCodewords,
+                                      bool bAllowRectangular);
 
   int32_t getSymbolDataWidth() const;
   int32_t getSymbolDataHeight() const;