diff --git a/clen_tools/sample_crystfel-ls.py b/clen_tools/sample_crystfel-ls.py
index 3993a9c..5878653 100644
--- a/clen_tools/sample_crystfel-ls.py
+++ b/clen_tools/sample_crystfel-ls.py
@@ -45,7 +45,7 @@ def h5_sample( lst, sample ):
 
     # write sample to file
     print( "writing to file" )
-    sample_file = "{0}_{1}.lst".format( lst_name, sample )
+    sample_file = "{0}_{1}".format( sample, lst_name )
     sample_df.to_csv( sample_file, sep=" ", index=False, header=False )
     print( "done" )
 
@@ -56,13 +56,15 @@ if __name__ == "__main__":
         "-l",
         "--list",
         help="give the path to SwissFEL daq list file",
-        type=str
+        type=str,
+        required=True
     )
     parser.add_argument(
         "-s",
         "--sample",
         help="number of random sample images to select",
-        type=int
+        type=int,
+        required=True
     )
     args = parser.parse_args()
     # run geom converter