diff --git a/src/ui/test/test.py b/src/ui/test/test.py
index 0df0223..be601ea 100755
--- a/src/ui/test/test.py
+++ b/src/ui/test/test.py
@@ -388,11 +388,13 @@ class Test(Widget):
             for i, step in enumerate(steps):
                 if step.type == "barcodes":
                     n_pieces = int(step.spec.get("n_pieces", 1))
-                    if n_pieces == 1:
+                    n_pieces_adapted = n_pieces
+                    if n_pieces_adapted == 1:
                         step.spec["barcode_name"] = 'serial'
                     else:
-                        step.spec["barcode_name"] = barcode_names[(n_pieces - 1) % len(barcode_names)]
-                        step.spec["n_pieces"] = str(n_pieces - 1)
+                        step.spec["barcode_name"] = barcode_names[(n_pieces_adapted - 1) % len(barcode_names)]
+                        n_pieces_adapted -= 1
+                        step.spec["n_pieces"] = str(n_pieces_adapted)
                         new_barcode_step = copy.deepcopy(step)  # create a deep copy of the step
                         steps.insert(i + 1, new_barcode_step)
                 if i in skip: