diff --git a/pyzebra/app/panel_ccl_integrate.py b/pyzebra/app/panel_ccl_integrate.py
index 53b7ba4..114ba35 100644
--- a/pyzebra/app/panel_ccl_integrate.py
+++ b/pyzebra/app/panel_ccl_integrate.py
@@ -162,14 +162,15 @@ def create():
 
     def upload_button_callback(_attr, _old, new):
         nonlocal det_data
-        for f_ind, f_str, f_name in enumerate(zip(new, upload_button.filename)):
+        det_data = []
+        for f_str, f_name in zip(new, upload_button.filename):
             with io.StringIO(base64.b64decode(f_str).decode()) as file:
                 base, ext = os.path.splitext(f_name)
                 file_data = pyzebra.parse_1D(file, ext)
 
             pyzebra.normalize_dataset(file_data, monitor_spinner.value)
 
-            if f_ind == 0:  # first file
+            if not det_data:  # first file
                 det_data = file_data
                 pyzebra.merge_duplicates(det_data)
                 js_data.data.update(fname=[base, base])
diff --git a/pyzebra/app/panel_param_study.py b/pyzebra/app/panel_param_study.py
index c10b18c..5452642 100644
--- a/pyzebra/app/panel_param_study.py
+++ b/pyzebra/app/panel_param_study.py
@@ -179,14 +179,14 @@ def create():
     def upload_button_callback(_attr, _old, new):
         nonlocal det_data
         det_data = []
-        for f_ind, f_str, f_name in enumerate(zip(new, upload_button.filename)):
+        for f_str, f_name in zip(new, upload_button.filename):
             with io.StringIO(base64.b64decode(f_str).decode()) as file:
                 base, ext = os.path.splitext(f_name)
                 file_data = pyzebra.parse_1D(file, ext)
 
             pyzebra.normalize_dataset(file_data, monitor_spinner.value)
 
-            if f_ind == 0:  # first file
+            if not det_data:  # first file
                 det_data = file_data
                 pyzebra.merge_duplicates(det_data)
                 js_data.data.update(fname=[base])