diff --git a/common/python/nomadcore/md_data_access/MDDataAccess.py b/common/python/nomadcore/md_data_access/MDDataAccess.py
index 53ef437740078cabd265267717de1d8c1a3d1170..1ae94c5eb3126d33e3a8940567c2f38ad67fdcd4 100644
--- a/common/python/nomadcore/md_data_access/MDDataAccess.py
+++ b/common/python/nomadcore/md_data_access/MDDataAccess.py
@@ -3384,7 +3384,7 @@ class MDDataAccess(object):
         """
         return self.trajhandler.cell_lengths
     
-    def load_pymolfile_topology(self, file_format):
+    def load_pymolfile_topology(self, file_format=None):
         """ function to call pymolfile topology reader
 
         Returns
@@ -3394,7 +3394,10 @@ class MDDataAccess(object):
 
         topology = None
         universe = None
-        fileformat = re.sub('[.]', '', file_format)
+        if file_format:
+            fileformat = re.sub('[.]', '', file_format)
+        else:
+            fileformat = file_format
         if self.topofile:
             try:
                 molfile_topo = pym.OpenMolfile(self.topofile, file_format=fileformat)