diff --git a/cpp/array_record_reader.cc b/cpp/array_record_reader.cc
index 8592112..bc7675e 100644
--- a/cpp/array_record_reader.cc
+++ b/cpp/array_record_reader.cc
@@ -313,6 +313,14 @@ void ArrayRecordReaderBase::Initialize() {
   }
 }
 
+uint64_t ArrayRecordReaderBase::ChunkStartOffset(uint64_t chunk_idx) const {
+  return state_->chunk_offsets[chunk_idx];
+}
+
+uint64_t ArrayRecordReaderBase::ChunkEndOffset(uint64_t chunk_idx) const {
+  return state_->ChunkEndOffset(chunk_idx);
+}
+
 absl::Status ArrayRecordReaderBase::ParallelReadRecords(
     absl::FunctionRef<absl::Status(uint64_t, absl::string_view)> callback)
     const {
@@ -591,7 +599,7 @@ uint64_t ArrayRecordReaderBase::NumRecords() const {
   return state_->num_records;
 }
 
-uint64_t ArrayRecordReaderBase::RecordGroupSize() {
+uint64_t ArrayRecordReaderBase::RecordGroupSize() const {
   if (!ok()) {
     return 0;
   }
diff --git a/cpp/array_record_reader.h b/cpp/array_record_reader.h
index d573e2f..3a9d011 100644
--- a/cpp/array_record_reader.h
+++ b/cpp/array_record_reader.h
@@ -244,7 +244,7 @@ class ArrayRecordReaderBase : public riegeli::Object {
   // Number of records in each compressed chunk configured at the file writing
   // stage by `ArrayRecordWriterBase::Options::set_group_size`. The acutal
   // number of records per group could be smaller equals to this number.
-  uint64_t RecordGroupSize();
+  uint64_t RecordGroupSize() const;
 
   // Index of the record to be read.
   uint64_t RecordIndex() const;
@@ -287,6 +287,8 @@ class ArrayRecordReaderBase : public riegeli::Object {
   ArrayRecordReaderBase& operator=(ArrayRecordReaderBase&& other) noexcept;
 
   void Initialize();
+  uint64_t ChunkStartOffset(uint64_t chunk_idx) const;
+  uint64_t ChunkEndOffset(uint64_t chunk_idx) const;
 
   virtual ThreadCompatibleSharedPtr<riegeli::Reader> get_backing_reader()
       const = 0;
diff --git a/python/testdata/digits.array_record-00000-of-00002 b/python/testdata/digits.array_record-00000-of-00002
index ca4fd6f..c52a248 100644
Binary files a/python/testdata/digits.array_record-00000-of-00002 and b/python/testdata/digits.array_record-00000-of-00002 differ
diff --git a/python/testdata/digits.array_record-00001-of-00002 b/python/testdata/digits.array_record-00001-of-00002
index 37223e5..d96ffbe 100644
Binary files a/python/testdata/digits.array_record-00001-of-00002 and b/python/testdata/digits.array_record-00001-of-00002 differ