diff --git a/sohstationviewer/controller/processing.py b/sohstationviewer/controller/processing.py
index 6ca57a1ca051e06170692163e8990bdf66427e98..4919363f4c5b043cf84e36c7352749477666a706 100644
--- a/sohstationviewer/controller/processing.py
+++ b/sohstationviewer/controller/processing.py
@@ -291,7 +291,7 @@ def get_data_type_from_file(
                 return 'RT130', False
             return None
 
-        if is_multiplex is None:
+        if is_multiplex in [None, False]:
             chans_in_stream.add(chan)
             if len(chans_in_stream) > 1:
                 is_multiplex = True