diff --git a/lisainstrument/instrument.py b/lisainstrument/instrument.py
index c1d9b62daeda182024419fdd7970882205ced487..7bc02c155569c94cd6ebd0d27d3096b3eaafb043 100755
--- a/lisainstrument/instrument.py
+++ b/lisainstrument/instrument.py
@@ -699,10 +699,12 @@ class Instrument:
         elif gws is None:
             logger.debug("No gravitational-wave responses")
             self.gw_file = None
+            self.gw_group = None
             self.gws = ForEachMOSA(0)
         else:
             logger.info("Using user-provided gravitational-wave responses")
             self.gw_file = None
+            self.gw_group = None
             self.gws = ForEachMOSA(gws)
 
     def _init_gw_file_before_1_1(self, gwf):