diff --git a/km3io/tools.py b/km3io/tools.py
index 16d81918378d3e6fe59baef03b51d96cc7f05181..641f4c4353fb0e1226591b3700d96a8b3455b965 100644
--- a/km3io/tools.py
+++ b/km3io/tools.py
@@ -48,8 +48,8 @@ class Branch:
         if subbranchmaps is not None:
             for mapper in subbranchmaps:
                 subbranch = self.__class__(self._tree,
-                                           mapper=mapper,
-                                           index=self._index)
+                                   mapper=mapper,
+                                   index=self._index)
                 self._subbranches.append(subbranch)
         for subbranch in self._subbranches:
             setattr(self, subbranch._mapper.name, subbranch)