diff --git a/common/python/nomadcore/parser_backend.py b/common/python/nomadcore/parser_backend.py
index f9e1b38529557f7f08b0211c396bfd6d145971fa..0108b74a81842d7570c57987a3eae34b6863842a 100644
--- a/common/python/nomadcore/parser_backend.py
+++ b/common/python/nomadcore/parser_backend.py
@@ -97,6 +97,8 @@ class JsonParseEventsWriterBackend(object):
             self.fileOut.write(", ")
         else:
             self.__writeComma = True
+        self.fileOut.flush() # Python3 uses buffer for IO operations. 
+        # Need to flush the buffer before accessing the content at json.dump
         json.dump(dic, self.fileOut, indent = 2, separators = (',', ':'), sort_keys=True) # default = self.__numpyEncoder)
 
     def startedParsingSession(self, mainFileUri, parserInfo, parserStatus = None, parserErrors = None):