diff --git a/pmodules_tools/db_diff/check.py b/pmodules_tools/db_diff/check.py
index 727f4edf..13597c76 100644
--- a/pmodules_tools/db_diff/check.py
+++ b/pmodules_tools/db_diff/check.py
@@ -103,8 +103,8 @@ def db_check_diff(current_pmodule_state, Pmodules_db_path, Pmodules_states):
         old_db = set(" ".join(i.split()) for i in old_pmodule_state.splitlines())
         all_module_list = list(current_db)
         all_module_list_sorted = sorted([x for x in all_module_list if 'stable' in x])
-        all_module_list_sorted.append(sorted([x for x in all_module_list if 'unstable' in x]))
-        all_module_list_sorted.append(sorted([x for x in all_module_list if 'deprecated' in x]))
+        all_module_list_sorted += sorted([x for x in all_module_list if 'unstable' in x]))
+        all_module_list_sorted += sorted([x for x in all_module_list if 'deprecated' in x]))
         all_module_list = all_module_list_sorted
 
         # We have to check the differences between the pmodule states.