diff --git a/src/cbptc19696.cpp b/src/cbptc19696.cpp
index 7746ba1..4751b8c 100644
--- a/src/cbptc19696.cpp
+++ b/src/cbptc19696.cpp
@@ -171,7 +171,7 @@ void CBPTC19696::decodeErrorCheck()
 }
 
 // Extract the 96 bits of payload
-void CBPTC19696::decodeExtractData(unsigned char* data)
+void CBPTC19696::decodeExtractData(unsigned char* data) const
 {
     bool bData[96U];
     unsigned int pos = 0U;
diff --git a/src/cbptc19696.h b/src/cbptc19696.h
index 7995da8..37d3a6e 100644
--- a/src/cbptc19696.h
+++ b/src/cbptc19696.h
@@ -36,7 +36,7 @@ private:
     void decodeExtractBinary(const unsigned char* in);
     void decodeErrorCheck();
     void decodeDeInterleave();
-    void decodeExtractData(unsigned char* data);
+    void decodeExtractData(unsigned char* data) const;
     
     void encodeExtractData(const unsigned char* in);
     void encodeInterleave();