diff --git a/viewer/widgets/PowderCalibrationWidget.cpp b/viewer/widgets/PowderCalibrationWidget.cpp
index 14dd62208..e1d11a4d2 100644
--- a/viewer/widgets/PowderCalibrationWidget.cpp
+++ b/viewer/widgets/PowderCalibrationWidget.cpp
@@ -80,8 +80,15 @@ std::vector<float> PowderCalibrationWidget::GetCalibrantRings() const {
     const auto &table = Calibrants();
     if (idx >= 0 && idx < static_cast<int>(table.size()))
         return CalibrantRings(table[idx].name);
-    if (sample_cell)
+    if (sample_cell) {
+        // With the group where the dataset has one: the absences then come from the symmetry rather
+        // than from a bare P-lattice assumption, and a centred cell's list no longer opens with a
+        // reflection that is not there - which would scale the whole calibration by the ratio between
+        // that ring and the first real one. Same call the CLI makes.
+        if (sample_sg)
+            return CalculateXtalRings(sample_cell.value(), *sample_sg);
         return CalculateXtalRings(sample_cell.value());
+    }
     return CalibrantRings(table.front().name);
 }
 
@@ -108,8 +115,10 @@ void PowderCalibrationWidget::updateCalibrantList() {
 }
 
 void PowderCalibrationWidget::loadImage(std::shared_ptr<const JFJochReaderImage> image) {
-    if (image)
+    if (image) {
         sample_cell = image->Dataset().experiment.GetUnitCell();
+        sample_sg = image->Dataset().experiment.GetGemmiSpaceGroup();
+    }
     updateCalibrantList();
 }
 
diff --git a/viewer/widgets/PowderCalibrationWidget.h b/viewer/widgets/PowderCalibrationWidget.h
index 699f7a54f..a4be9cc23 100644
--- a/viewer/widgets/PowderCalibrationWidget.h
+++ b/viewer/widgets/PowderCalibrationWidget.h
@@ -4,6 +4,7 @@
 #pragma once
 
 #include <QWidget>
+#include <gemmi/symmetry.hpp>
 #include <QCheckBox>
 #include <QComboBox>
 #include <QVector>
@@ -26,6 +27,9 @@ struct CalibrationSelection {
 class PowderCalibrationWidget : public QWidget {
     Q_OBJECT
     std::optional<UnitCell> sample_cell;
+    // Taken with the cell, and used with it: the ring list a user-supplied cell produces has to carry
+    // the group's absences, or the fit pairs the innermost OBSERVED ring with a forbidden one.
+    std::optional<gemmi::SpaceGroup> sample_sg;
 
     QComboBox* calibrantCombo{nullptr}; // stores current calibrant selection
     QComboBox* methodCombo{nullptr};    // rings / spots, for the whole-dataset run