diff --git a/reader/JFJochHDF5Reader.cpp b/reader/JFJochHDF5Reader.cpp
index cefbba4e..e6d639c8 100644
--- a/reader/JFJochHDF5Reader.cpp
+++ b/reader/JFJochHDF5Reader.cpp
@@ -308,7 +308,11 @@ void JFJochHDF5Reader::ReadFile(const std::string &filename) {
                 dataset->bkg_estimate = master_file->ReadOptVector<float>("/entry/MX/bkgEstimate");
                 dataset->resolution_estimate = master_file->ReadOptVector<float>("/entry/MX/resolutionEstimate");
                 dataset->profile_radius = master_file->ReadOptVector<float>("/entry/MX/profileRadius");
-                dataset->indexing_lattice_count = master_file->ReadOptVector<float>("/entry/MX/indexingLatticeCount");
+                // Master files write indexedLatticeCount; data files / the per-file MX
+                // plugin use indexingLatticeCount. Accept either for backward compatibility.
+                dataset->indexing_lattice_count = master_file->ReadOptVector<float>("/entry/MX/indexedLatticeCount");
+                if (dataset->indexing_lattice_count.empty())
+                    dataset->indexing_lattice_count = master_file->ReadOptVector<float>("/entry/MX/indexingLatticeCount");
                 dataset->mosaicity_deg = master_file->ReadOptVector<float>("/entry/MX/mosaicity");
                 dataset->b_factor = master_file->ReadOptVector<float>("/entry/MX/bFactor");
                 dataset->image_scale_factor = master_file->ReadOptVector<float>("/entry/MX/imageScaleFactor");