diff --git a/modoboa_installer/scripts/base.py b/modoboa_installer/scripts/base.py
index b6faf0e..138fef4 100644
--- a/modoboa_installer/scripts/base.py
+++ b/modoboa_installer/scripts/base.py
@@ -173,6 +173,7 @@ class Installer:
         if self.with_db:
             self._dump_database(path)
         custom_backup_path = os.path.join(path, "custom", self.appname)
+        utils.mkdir_safe(custom_backup_path)
         self.custom_backup(custom_backup_path)
 
     def custom_backup(self, path):
diff --git a/modoboa_installer/scripts/opendkim.py b/modoboa_installer/scripts/opendkim.py
index 3b9b239..8b6e253 100644
--- a/modoboa_installer/scripts/opendkim.py
+++ b/modoboa_installer/scripts/opendkim.py
@@ -135,5 +135,7 @@ class Opendkim(base.Installer):
     def custom_backup(self, path):
         """Backup DKIM keys."""
         if os.path.isdir(self.app_config["keys_storage_dir"]):
-            shutil.copytree(self.app_config["keys_storage_dir"], path)
+            shutil.copytree(
+                self.app_config["keys_storage_dir"], path, dirs_exist_ok=True
+            )
             utils.printcolor("DKIM keys saved!", utils.GREEN)