diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 15532abd..1e0d37c3 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -18,6 +18,7 @@ This is an UNSTABLE release. It includes many experimental features, as well as
 * HDF5 and image stream: `mirror_y` records whether the assembled image is mirrored in Y relative to the detector's raw readout.
 * rugnux: an image integrated in pyFAI through the `.poni` file written by `--mode calibration` now comes out with the correct azimuth. Radial integration is unchanged.
 * rugnux: the `.poni` file declares pyFAI's `orientation`, which needs pyFAI 2024.01 or newer.
+* rugnux: fixing the space group with `-S` no longer prevents the lattice from being found; the group is applied to scaling and merging rather than to the indexing search.
 * rugnux: the detector geometry is also logged in XDS's convention (`ORGX`/`ORGY`, detector axis vectors, rotation axis), so it can be compared with an XDS refinement.
 * rugnux: `_process.h5` describes the pixel format of the images it links to.
 * A DECTRIS detector sending signed images is no longer declared unsigned in the image stream and in HDF5.
diff --git a/image_analysis/rotation_indexer/RotationIndexer.cpp b/image_analysis/rotation_indexer/RotationIndexer.cpp
index 8b2c62e3..89b8e898 100644
--- a/image_analysis/rotation_indexer/RotationIndexer.cpp
+++ b/image_analysis/rotation_indexer/RotationIndexer.cpp
@@ -143,33 +143,24 @@ void RotationIndexer::RunIndexing() {
     const auto indexer_result = indexer_.Run(experiment, coords);
 
     if (!indexer_result.lattice.empty() && indexer_result.lattice[0].CalcVolume() > 1.0) {
-        auto sg = experiment.GetGemmiSpaceGroup();
         DiffractionExperiment experiment_copy(experiment);
         const float index_tol = experiment.GetIndexingSettings().GetTolerance();
         const auto orig_axis = axis_;
 
-        // Map an FFT candidate cell to a (metric) space-group setting: the user-fixed SG's conventional
-        // cell, or the de-novo Bravais lattice. Re-express a metrically-hexagonal cell in conventional
-        // hexagonal axes (LatticeSearch can land on the ortho-hexagonal C setting) so the 3-fold is not
-        // hidden from scaling.
+        // Map an FFT candidate cell to its Bravais lattice. Re-express a metrically-hexagonal cell in
+        // conventional hexagonal axes (LatticeSearch can land on the ortho-hexagonal C setting) so the
+        // 3-fold is not hidden from scaling.
+        //
+        // A user-fixed space group is deliberately NOT stamped on here. The group names the symmetry;
+        // it does not say which basis the FFT candidate came back in, and the conventional cell above
+        // was reduced for whatever class the METRIC matched. Relabelling that cell with the group's
+        // system and centring leaves the constrained refine snapping the wrong angles to the ideal
+        // ones: measured, a C-centred orthorhombic cell relabelled primitive monoclinic indexed 1 of
+        // 60 validation frames and an F-cubic one relabelled trigonal indexed 0 of 60, where the same
+        // frames index at 36/60 and 51/60 without a group. The group is applied where it belongs - to
+        // the scaling and the merge.
         auto build_sr = [&](const CrystalLattice &cand) -> LatticeSearchResult {
             auto ls = LatticeSearch(cand);
-            if (sg) {
-                const auto is_hexagonal = [](gemmi::CrystalSystem s) {
-                    return s == gemmi::CrystalSystem::Trigonal || s == gemmi::CrystalSystem::Hexagonal;
-                };
-                CrystalLattice conventional = ls.conventional;
-                if (is_hexagonal(sg->crystal_system()) && !is_hexagonal(ls.system))
-                    conventional = HexagonalConventional(ls.primitive_reduced);
-                return LatticeSearchResult{
-                    .niggli_class = ls.niggli_class,
-                    .primitive_reduced = ls.primitive_reduced,
-                    .conventional = conventional,
-                    .system = sg->crystal_system(),
-                    .centering = sg->centring_type(),
-                    .reindex = ls.reindex,
-                };
-            }
             if (!IsHexagonalSystem(ls.system) && IsMetricallyHexagonal(ls.primitive_reduced)) {
                 ls.conventional = HexagonalConventional(ls.primitive_reduced);
                 ls.system = gemmi::CrystalSystem::Hexagonal;
@@ -250,9 +241,12 @@ void RotationIndexer::RunIndexing() {
             const auto conv_uc = w.sr.conventional.GetUnitCell();
             const float length_bound_A = 1.2f * static_cast<float>(std::max({conv_uc.a, conv_uc.b, conv_uc.c}));
             w.constrained = make_data(w.sr.conventional, w.sr.system, length_bound_A);
-            // Pseudo-symmetry guard (de-novo only - never override a user-fixed space group): also refine
-            // unconstrained (triclinic) on the primitive cell.
-            w.has_tri = (!sg && w.sr.system != gemmi::CrystalSystem::Triclinic);
+            // Pseudo-symmetry guard: also refine unconstrained (triclinic) on the primitive cell. Run it
+            // with a user-fixed space group too. The metric promotion the constrained refine acts on is
+            // decided by the geometry, not by the group, so it can be false whether or not a group was
+            // given - and without this cell there is nothing to catch it with, which is how a fixed
+            // group turned crystals the de-novo path indexes at 60/60 into runs that index none.
+            w.has_tri = (w.sr.system != gemmi::CrystalSystem::Triclinic);
             if (w.has_tri)
                 w.tri = make_data(w.sr.primitive_reduced, gemmi::CrystalSystem::Triclinic, length_bound_A);
             w.viable = true;