diff --git a/lisainstrument/instrument.py b/lisainstrument/instrument.py
index 2b088172cefc91f927b7ac59bdb98f2f7052a017..0ed00d2cbd532b5aa5c7f0318878e822bdcb96a7 100644
--- a/lisainstrument/instrument.py
+++ b/lisainstrument/instrument.py
@@ -510,7 +510,8 @@ class Instrument:
             but: optional category of noises to keep on ['laser', 'modulation',
                 'clock', 'pathlength', 'ranging', 'jitters']
         """
-        if but not in ['laser', 'modulation', 'clock', 'pathlength', 'ranging', 'jitters']:
+        valid_noises = ['laser', 'modulation', 'clock', 'pathlength', 'ranging', 'jitters']
+        if but is not None and but not in valid_noises:
             raise ValueError(f"unknown noise '{but}'")
 
         if but != 'laser':