diff --git a/nifty5/operators/block_diagonal_operator.py b/nifty5/operators/block_diagonal_operator.py
index 1ac8abe8fd0385d79bc8462dcd917daf540be676..0996983350b2df9def4980f0b4fcf4e8a255eee0 100644
--- a/nifty5/operators/block_diagonal_operator.py
+++ b/nifty5/operators/block_diagonal_operator.py
@@ -27,7 +27,7 @@ class BlockDiagonalOperator(EndomorphicOperator):
     domain : MultiDomain
         Domain and target of the operator.
     operators : dict
-        Dictionary with subdomain names as keys and :class:`LinearOperator`s
+        Dictionary with subdomain names as keys and :class:`LinearOperator` s
         as items.
     """
     def __init__(self, domain, operators):