diff --git a/backend/genesys/device.cpp b/backend/genesys/device.cpp
index 88dd5dd08..6eee06ef7 100644
--- a/backend/genesys/device.cpp
+++ b/backend/genesys/device.cpp
@@ -239,7 +239,6 @@ std::ostream& operator<<(std::ostream& out, const Genesys_Device& dev)
         << static_cast<unsigned>(dev.control[4]) << ' '
         << static_cast<unsigned>(dev.control[5]) << '\n' << std::dec
         << "    average_size: " << dev.average_size << '\n'
-        << "    calib_total_bytes_to_read: " << dev.calib_total_bytes_to_read << '\n'
         << "    calib_session: " << format_indent_braced_list(4, dev.calib_session) << '\n'
         << "    gamma_override_tables[0].size(): " << dev.gamma_override_tables[0].size() << '\n'
         << "    gamma_override_tables[1].size(): " << dev.gamma_override_tables[1].size() << '\n'
diff --git a/backend/genesys/device.h b/backend/genesys/device.h
index 53fbd0476..04b53727f 100644
--- a/backend/genesys/device.h
+++ b/backend/genesys/device.h
@@ -269,8 +269,6 @@ struct Genesys_Device
     std::uint8_t control[6] = {};
 
     size_t average_size = 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;
diff --git a/backend/genesys/genesys.cpp b/backend/genesys/genesys.cpp
index 6574f72b1..632412e58 100644
--- a/backend/genesys/genesys.cpp
+++ b/backend/genesys/genesys.cpp
@@ -1690,11 +1690,9 @@ static void genesys_shading_calibration_impl(Genesys_Device* dev, const Genesys_
     }
 
     // FIXME: the current calculation is likely incorrect on non-GL843 implementations,
-    // but this needs checking
-    if (dev->calib_total_bytes_to_read > 0) {
-        size = dev->calib_total_bytes_to_read;
-    } else if (dev->model->asic_type == AsicType::GL843) {
-        size = channels * 2 * pixels_per_line * dev->calib_session.params.lines;
+    // but this needs checking. Note the extra line when computing size.
+    if (dev->model->asic_type == AsicType::GL843) {
+        size = dev->calib_session.output_total_bytes_raw;
     } else {
         size = channels * 2 * pixels_per_line * (dev->calib_session.params.lines + 1);
     }
@@ -1941,8 +1939,8 @@ static void genesys_dark_white_shading_calibration(Genesys_Device* dev,
   dev->dark_average_data.clear();
   dev->dark_average_data.resize(dev->average_size);
 
-    if (dev->calib_total_bytes_to_read > 0) {
-        size = dev->calib_total_bytes_to_read;
+    if (dev->model->asic_type == AsicType::GL843) {
+        size = dev->calib_session.output_total_bytes_raw;
     } else {
         size = channels * 2 * pixels_per_line * dev->calib_session.params.lines;
     }
diff --git a/backend/genesys/gl124.cpp b/backend/genesys/gl124.cpp
index 5b8d79ff6..994fe952c 100644
--- a/backend/genesys/gl124.cpp
+++ b/backend/genesys/gl124.cpp
@@ -1194,7 +1194,6 @@ void CommandSetGl124::init_regs_for_shading(Genesys_Device* dev, const Genesys_S
 
     const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution, channels,
                                                          dev->settings.scan_method);
-  dev->calib_total_bytes_to_read = 0;
     factor = calib_sensor.optical_res / resolution;
 
   /* distance to move to reach white target at high resolution */
diff --git a/backend/genesys/gl843.cpp b/backend/genesys/gl843.cpp
index 3e5cbcd11..0b546af6f 100644
--- a/backend/genesys/gl843.cpp
+++ b/backend/genesys/gl843.cpp
@@ -1770,7 +1770,6 @@ void CommandSetGl843::init_regs_for_shading(Genesys_Device* dev, const Genesys_S
     init_regs_for_scan_session(dev, calib_sensor, &regs, session);
 
     dev->calib_session = session;
-    dev->calib_total_bytes_to_read = session.output_total_bytes_raw;
 }
 
 /** @brief set up registers for the actual scan
diff --git a/backend/genesys/gl846.cpp b/backend/genesys/gl846.cpp
index 49a10ae5e..7d10fe35f 100644
--- a/backend/genesys/gl846.cpp
+++ b/backend/genesys/gl846.cpp
@@ -963,7 +963,6 @@ void CommandSetGl846::init_regs_for_shading(Genesys_Device* dev, const Genesys_S
 
     const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution, channels,
                                                          dev->settings.scan_method);
-  dev->calib_total_bytes_to_read = 0;
     unsigned calib_lines = dev->model->shading_lines;
     if (resolution == 4800) {
         calib_lines *= 2;
diff --git a/backend/genesys/gl847.cpp b/backend/genesys/gl847.cpp
index 21e7ea4f7..c972a7ac9 100644
--- a/backend/genesys/gl847.cpp
+++ b/backend/genesys/gl847.cpp
@@ -972,7 +972,6 @@ void CommandSetGl847::init_regs_for_shading(Genesys_Device* dev, const Genesys_S
     const auto& calib_sensor = sanei_genesys_find_sensor(dev, resolution, channels,
                                                          dev->settings.scan_method);
 
-  dev->calib_total_bytes_to_read = 0;
     unsigned calib_lines = dev->model->shading_lines;
     if (resolution == 4800) {
         calib_lines *= 2;