diff --git a/bzip_extent_writer.cc b/bzip_extent_writer.cc
index 9d432c7..b4f864f 100644
--- a/bzip_extent_writer.cc
+++ b/bzip_extent_writer.cc
@@ -9,7 +9,7 @@
 namespace chromeos_update_engine {
 
 namespace {
-const vector<char>::size_type kOutputBufferLength = 1024 * 1024;
+const vector<char>::size_type kOutputBufferLength = 16 * 1024;
 }
 
 bool BzipExtentWriter::Init(int fd,
@@ -28,39 +28,45 @@
 bool BzipExtentWriter::Write(const void* bytes, size_t count) {
   vector<char> output_buffer(kOutputBufferLength);
 
-  const char* c_bytes = reinterpret_cast<const char*>(bytes);
+  // Copy the input data into |input_buffer_| only if |input_buffer_| already
+  // contains unconsumed data. Otherwise, process the data directly from the
+  // source.
+  const char* input = reinterpret_cast<const char*>(bytes);
+  const char* input_end = input + count;
+  if (!input_buffer_.empty()) {
+    input_buffer_.insert(input_buffer_.end(), input, input_end);
+    input = &input_buffer_[0];
+    input_end = input + input_buffer_.size();
+  }
+  stream_.next_in = const_cast<char*>(input);
+  stream_.avail_in = input_end - input;
 
-  input_buffer_.insert(input_buffer_.end(), c_bytes, c_bytes + count);
-  
-  stream_.next_in = &input_buffer_[0];
-  stream_.avail_in = input_buffer_.size();
-  
   for (;;) {
     stream_.next_out = &output_buffer[0];
     stream_.avail_out = output_buffer.size();
 
     int rc = BZ2_bzDecompress(&stream_);
     TEST_AND_RETURN_FALSE(rc == BZ_OK || rc == BZ_STREAM_END);
-    
+
     if (stream_.avail_out == output_buffer.size())
       break;  // got no new bytes
-    
+
     TEST_AND_RETURN_FALSE(
         next_->Write(&output_buffer[0],
                      output_buffer.size() - stream_.avail_out));
-    
+
     if (rc == BZ_STREAM_END)
       CHECK_EQ(stream_.avail_in, static_cast<unsigned int>(0));
     if (stream_.avail_in == 0)
       break;  // no more input to process
   }
 
-  // store unconsumed data in input_buffer_.
-  
-  vector<char> new_input_buffer(input_buffer_.end() - stream_.avail_in,
-                                input_buffer_.end());
-  new_input_buffer.swap(input_buffer_);
-  
+  // Store unconsumed data (if any) in |input_buffer_|.
+  if (stream_.avail_in || !input_buffer_.empty()) {
+    vector<char> new_input_buffer(input_end - stream_.avail_in, input_end);
+    new_input_buffer.swap(input_buffer_);
+  }
+
   return true;
 }
 
diff --git a/bzip_extent_writer_unittest.cc b/bzip_extent_writer_unittest.cc
index d724bc4..38ba117 100644
--- a/bzip_extent_writer_unittest.cc
+++ b/bzip_extent_writer_unittest.cc
@@ -53,8 +53,8 @@
   extents.push_back(extent);
 
   // 'echo test | bzip2 | hexdump' yields:
-  const char test_uncompressed[] = "test\n";
-  unsigned char test[] = {
+  static const char test_uncompressed[] = "test\n";
+  static const unsigned char test[] = {
     0x42, 0x5a, 0x68, 0x39, 0x31, 0x41, 0x59, 0x26, 0x53, 0x59, 0xcc, 0xc3,
     0x71, 0xd4, 0x00, 0x00, 0x02, 0x41, 0x80, 0x00, 0x10, 0x02, 0x00, 0x0c,
     0x00, 0x20, 0x00, 0x21, 0x9a, 0x68, 0x33, 0x4d, 0x19, 0x97, 0x8b, 0xb9,
@@ -101,12 +101,16 @@
   BzipExtentWriter bzip_writer(&direct_writer);
   EXPECT_TRUE(bzip_writer.Init(fd(), extents, kBlockSize));
 
+  vector<char> original_compressed_data = compressed_data;
   for (vector<char>::size_type i = 0; i < compressed_data.size();
        i += kChunkSize) {
     size_t this_chunk_size = min(kChunkSize, compressed_data.size() - i);
     EXPECT_TRUE(bzip_writer.Write(&compressed_data[i], this_chunk_size));
   }
   EXPECT_TRUE(bzip_writer.End());
+
+  // Check that the const input has not been clobbered.
+  ExpectVectorsEq(original_compressed_data, compressed_data);
   
   vector<char> output(kDecompressedLength + 1);
   ssize_t bytes_read = pread(fd(), &output[0], output.size(), 0);