diff --git a/nifty4/sugar.py b/nifty4/sugar.py
index 0dd0be5d8e3af5a25e3519fde6606d62ae082ded..33db00de2fd61a3498e43654ef4eb2a0f222429b 100644
--- a/nifty4/sugar.py
+++ b/nifty4/sugar.py
@@ -21,6 +21,7 @@ import numpy as np
 from .domains.power_space import PowerSpace
 from .field import Field
 from .multi.multi_field import MultiField
+from .multi.block_diagonal_operator import BlockDiagonalOperator
 from .multi.multi_domain import MultiDomain
 from .operators.diagonal_operator import DiagonalOperator
 from .operators.scaling_operator import ScalingOperator