diff --git a/backend/genesys.cc b/backend/genesys.cc
index f36dd3242..d8bbf5706 100644
--- a/backend/genesys.cc
+++ b/backend/genesys.cc
@@ -1594,6 +1594,9 @@ static void genesys_shading_calibration_impl(Genesys_Device* dev, const Genesys_
                                              bool is_dark, const std::string& log_filename_prefix)
 {
     DBG_HELPER(dbg);
+
+    debug_dump(DBG_info, dev->calib_session);
+
   size_t size;
   uint32_t pixels_per_line;
   uint8_t channels;
diff --git a/backend/genesys_device.h b/backend/genesys_device.h
index 25078ce3a..00414a840 100644
--- a/backend/genesys_device.h
+++ b/backend/genesys_device.h
@@ -257,6 +257,10 @@ struct Genesys_Device
     size_t calib_resolution = 0;
      // bytes to read from USB when calibrating. If 0, this is not set
     size_t calib_total_bytes_to_read = 0;
+
+    // the session that was configured for calibration
+    ScanSession calib_session;
+
     // certain scanners support much higher resolution when scanning transparency, but we can't
     // read whole width of the scanner as a single line at that resolution. Thus for stuff like
     // calibration we want to read only the possible calibration area.
diff --git a/backend/genesys_gl843.cc b/backend/genesys_gl843.cc
index 15b643438..fd254f819 100644
--- a/backend/genesys_gl843.cc
+++ b/backend/genesys_gl843.cc
@@ -2269,6 +2269,7 @@ static void gl843_init_regs_for_shading(Genesys_Device* dev, const Genesys_Senso
   // the pixel number may be updated to conform to scanner constraints
   dev->calib_pixels = dev->current_setup.pixels;
 
+    dev->calib_session = session;
     dev->calib_total_bytes_to_read = session.output_total_bytes_raw;
 
   dev->scanhead_position_in_steps += dev->calib_lines + move;