diff --git a/exasol/driver/websocket/_connection.py b/exasol/driver/websocket/_connection.py
index 20c1944b..2d51a71a 100644
--- a/exasol/driver/websocket/_connection.py
+++ b/exasol/driver/websocket/_connection.py
@@ -119,12 +119,13 @@ def connection(self):
 
     def close(self):
         """See also :py:meth: `Connection.close`"""
-        if not self._connection:
+        if self._connection is None or self._connection.is_closed:
             return
         try:
             self._connection.close()
         except Exception as ex:
             raise Error() from ex
+        self._connection = None
 
     @_requires_connection
     def commit(self):