diff --git a/writer/HDF5DataFilePluginMX.cpp b/writer/HDF5DataFilePluginMX.cpp
index 758835f8..f9c7cb5d 100644
--- a/writer/HDF5DataFilePluginMX.cpp
+++ b/writer/HDF5DataFilePluginMX.cpp
@@ -127,7 +127,7 @@ void HDF5DataFilePluginMX::Write(const DataMessage &msg, uint64_t image_number)
         if (indexing)
             spot_indexed.resize(max_spots * (max_image_number + 1));
         if (indexing)
-            indexed_lattice.resize((max_image_number + 1) * 9);
+            indexed_lattice.resize((max_image_number + 1) * 9, NAN);
     }
 
     uint32_t spot_cnt = std::min(msg.spots.size(), max_spots);