diff --git a/src/spikeinterface/core/sortinganalyzer.py b/src/spikeinterface/core/sortinganalyzer.py
index d57df2b5ae..b78a346c02 100644
--- a/src/spikeinterface/core/sortinganalyzer.py
+++ b/src/spikeinterface/core/sortinganalyzer.py
@@ -921,11 +921,11 @@ def compute_one_extension(self, extension_name, save=True, **kwargs):
         >>> wfs = compute_waveforms(sorting_analyzer, **some_params)
 
         """
+        extension_class = get_extension_class(extension_name)
+
         for child in _get_children_dependencies(extension_name):
             self.delete_extension(child)
 
-        extension_class = get_extension_class(extension_name)
-
         if extension_class.need_job_kwargs:
             params, job_kwargs = split_job_kwargs(kwargs)
         else: