diff --git a/payload_consumer/xor_extent_writer.cc b/payload_consumer/xor_extent_writer.cc
index fe7eca7..d4f6252 100644
--- a/payload_consumer/xor_extent_writer.cc
+++ b/payload_consumer/xor_extent_writer.cc
@@ -28,7 +28,7 @@
 bool XORExtentWriter::WriteXorCowOp(const uint8_t* bytes,
                                     const size_t size,
                                     const Extent& xor_ext,
-                                    const size_t src_offset) {
+                                    const uint64_t src_offset) {
   xor_block_data.resize(BlockSize() * xor_ext.num_blocks());
   const auto src_block = src_offset / BlockSize();
   ssize_t bytes_read = 0;
diff --git a/payload_consumer/xor_extent_writer.h b/payload_consumer/xor_extent_writer.h
index 2074ee2..ea270bc 100644
--- a/payload_consumer/xor_extent_writer.h
+++ b/payload_consumer/xor_extent_writer.h
@@ -63,13 +63,13 @@
   bool WriteXorCowOp(const uint8_t* bytes,
                      const size_t size,
                      const Extent& xor_ext,
-                     size_t src_offset);
+                     uint64_t src_offset);
   const google::protobuf::RepeatedPtrField<Extent>& src_extents_;
   const FileDescriptorPtr source_fd_;
   const ExtentMap<const CowMergeOperation*>& xor_map_;
   android::snapshot::ICowWriter* cow_writer_;
   std::vector<uint8_t> xor_block_data;
-  const size_t partition_size_;
+  const uint64_t partition_size_;
 };
 
 }  // namespace chromeos_update_engine