diff --git a/backup.py b/backup.py
index f49129e..a202d8c 100644
--- a/backup.py
+++ b/backup.py
@@ -8,6 +8,7 @@ import tarfile
 import sqlite3
 import pathlib
 import hashlib
+import collections as coll
 
 from b2sdk.v2 import B2Api
 from crypt import encrypt_file, decrypt_file
@@ -287,11 +288,10 @@ class DataBase:
                 crypt_id_list.append(cursor.fetchone()['crypt_id'])
             except TypeError:
                 pass
-        try:
-            if len(list(set(crypt_id_list))) == 1:
-                return crypt_id_list[0]
-            id = most_frequent(crypt_id_list)
-        except ValueError:
+        if len(crypt_id_list) != 0:
+            id = most_common(crypt_id_list)
+        else:
+            # if not already/find in bdd
             cursor.execute("""SELECT IFNULL(max(id) + 1, 0) as crypt_id FROM crypt""")
             return cursor.fetchone()['crypt_id']
         params = {'id': id,
@@ -302,13 +302,16 @@ class DataBase:
             AND name NOT IN ({name})
             AND path NOT IN ({path})""".format(**params))
         neighbour = cursor.fetchall()
+        # if they have a neighbour don't overwrite it
         if len(neighbour) > 0:
             cursor.execute("""SELECT IFNULL(max(id) + 1, 0) as crypt_id FROM crypt""")
             return cursor.fetchone()['crypt_id']
         else:
-            cursor.execute("""UPDATE files SET crypt_id={id}
-                WHERE name IN ({name})
-                AND path IN ({path})""".format(**params))
+            # if they are different, define the same id for the files of this archive
+            if len(set(crypt_id_list)) > 1:
+                cursor.execute("""UPDATE files SET crypt_id={id}
+                    WHERE name IN ({name})
+                    AND path IN ({path})""".format(**params))
             return id
 
     def exist(self, file):
@@ -389,6 +392,18 @@ def most_frequent(list):
     return max(set(list), key=list.count)
 
 
+def most_common(lst):
+    if len(set(lst)) == 1:
+        return lst[0]
+    data = coll.Counter(lst)
+    most = {'count': 0, 'item': 99999}
+    for item, count in data.items():
+        if count > most['count'] and item < most['item']:
+            most['count'] = count
+            most['item'] = item
+    return most['item']
+
+
 def dict_factory(cursor, row):
     d = {}
     for idx, col in enumerate(cursor.description):