diff --git a/src/laszipper.cpp b/src/laszipper.cpp
index 5bf912c..f7d5b39 100644
--- a/src/laszipper.cpp
+++ b/src/laszipper.cpp
@@ -76,7 +76,6 @@ size_t LasZipper::compress(py::buffer &buffer)
     while (num_points_in_buffer != 0)
     {
         m_is.seekp(0);
-        m_is.seekg(0);
 
         py::ssize_t num_points_for_this_iter =
             std::min(num_points_in_buffer, max_points_before_filling_stream);
@@ -84,6 +83,8 @@ size_t LasZipper::compress(py::buffer &buffer)
             num_points_for_this_iter * static_cast<size_t>(m_header->point_data_record_length);
         m_is.write(in_ptr, num_bytes_for_this_iter);
 
+        m_is.seekg(0);
+
         for (size_t i{0}; i < num_points_for_this_iter; ++i)
         {
             if (laszip_read_point(m_reader))
@@ -107,7 +108,7 @@ size_t LasZipper::compress(py::buffer &buffer)
             }
         }
 
-        in_ptr += num_points_for_this_iter;
+        in_ptr += num_bytes_for_this_iter;
         num_points_in_buffer -= num_points_for_this_iter;
     }