diff --git a/rugnux/Rugnux.cpp b/rugnux/Rugnux.cpp
index 00efab99..8ef1e368 100644
--- a/rugnux/Rugnux.cpp
+++ b/rugnux/Rugnux.cpp
@@ -835,12 +835,22 @@ ProcessResult Rugnux::RunPipeline(RugnuxObserver *observer, bool write_output, b
             // frame in six, several times below the weakest crystal that still merges. It is checked AFTER
             // the long-axis rescue, so a metric that rescue recovers is never rejected on its pre-rescue
             // score.
-            if (best.score < static_cast<int>(validation.size()) / 6)
+            if (best.score < static_cast<int>(validation.size()) / 6) {
+                // Name the cell and Bravais class that was rejected. The commonest cause is a metric
+                // symmetry promoted one class too far - the constrained cell then misses every
+                // reflection by the small angle the constraint snapped away - and without the cell in
+                // the message there is nothing to see that from.
+                const auto &c = best.result->search_result.conventional.GetUnitCell();
                 throw JFJochException(JFJochExceptionCategory::InputParameterInvalid,
                                       fmt::format("Two-pass rotation indexing found only a lattice that "
                                                   "indexes {}/{} validation frames - too few for it to be "
-                                                  "this crystal's lattice.{}",
-                                                  best.score, static_cast<int>(validation.size()), next_steps));
+                                                  "this crystal's lattice. It was {}-centred {}, "
+                                                  "{:.2f} {:.2f} {:.2f} {:.2f} {:.2f} {:.2f}.{}",
+                                                  best.score, static_cast<int>(validation.size()),
+                                                  best.result->search_result.centering,
+                                                  gemmi::crystal_system_str(best.result->search_result.system),
+                                                  c.a, c.b, c.c, c.alpha, c.beta, c.gamma, next_steps));
+            }
             indexer->ForceRotationIndexerResult(*best.result);
             logger.Info("Two-pass rotation indexing found lattice (scheme '{}': {}/{} validation frames)",
                         best.name, best.score, static_cast<int>(validation.size()));