diff --git a/common/python/nomadcore/md_data_access/MDDataAccess.py b/common/python/nomadcore/md_data_access/MDDataAccess.py
index f31056e50c87c6c226f541051f19ea2f3ea9cf32..53ef437740078cabd265267717de1d8c1a3d1170 100644
--- a/common/python/nomadcore/md_data_access/MDDataAccess.py
+++ b/common/python/nomadcore/md_data_access/MDDataAccess.py
@@ -4519,7 +4519,7 @@ class MDDataAccess(object):
             self.topocode is not None):
             topocode = self.topocode
         n_atoms=None
-        if self.topohandler is not None:
+        if self.topohandler is not None and topocode is not None:
             if "gromosread" in topocode:
                 n_atoms = len(self.topohandler.atoms)
             elif "pymolfile" in topocode: