diff --git a/src/fountain-decoder.cpp b/src/fountain-decoder.cpp
index e236062..916df45 100644
--- a/src/fountain-decoder.cpp
+++ b/src/fountain-decoder.cpp
@@ -25,7 +25,7 @@ FountainDecoder::Part::Part(const FountainEncoder::Part& p)
 {
 }
 
-FountainDecoder::Part::Part(PartIndexes& indexes, ByteVector& data)
+FountainDecoder::Part::Part(PartIndexes& indexes, const ByteVector& data)
     : indexes_(indexes)
     , data_(data)
 {
diff --git a/src/fountain-decoder.hpp b/src/fountain-decoder.hpp
index 6dc92d7..140d684 100644
--- a/src/fountain-decoder.hpp
+++ b/src/fountain-decoder.hpp
@@ -52,7 +52,7 @@ class FountainDecoder final {
 
     public:
         explicit Part(const FountainEncoder::Part& p);
-        Part(PartIndexes& indexes, ByteVector& data);
+        Part(PartIndexes& indexes, const ByteVector& data);
 
         const PartIndexes& indexes() const { return indexes_; }
         const ByteVector& data() const { return data_; }