diff --git a/src/toolbox_scs/misc/bunch_pattern.py b/src/toolbox_scs/misc/bunch_pattern.py
index 34ba18c67204b1ee46dc67e70b734b496b0576e4..57a5f40aeced164b6161d191612f7e156a5c9e84 100644
--- a/src/toolbox_scs/misc/bunch_pattern.py
+++ b/src/toolbox_scs/misc/bunch_pattern.py
@@ -35,7 +35,7 @@ def npulses_has_changed(run, sase='sase3', run_mnemonics=None):
     """
     Checks if the number of pulses has changed during the run for
     a specific location `sase` (='sase1', 'sase3', 'scs_ppl' or 'laser')
-    If the source is not found, returns True.
+    If the source is not found in the run, returns True.
 
     Parameters
     ----------
@@ -52,6 +52,10 @@ def npulses_has_changed(run, sase='sase3', run_mnemonics=None):
         True if the number of pulses has changed or the source was not
         found, False if the number of pulses did not change.
     """
+    sase_list = ['sase1', 'sase3', 'laser', 'scs_ppl']
+    if sase not in sase_list:
+        raise ValueError(f"Unknow sase location '{sase}'. Expected one in"
+                         f"{sase_list}")
     if run_mnemonics is None:
         run_mnemonics = mnemonics_for_run(run)
     if sase == 'scs_ppl':