diff --git a/nifty5/multi/block_diagonal_operator.py b/nifty5/multi/block_diagonal_operator.py
index 0546f35a1a89b99eb8dfd1258a1770805f49225e..3d9ec9fc32d9ca2dca5bddc2077b8e6a11814fdc 100644
--- a/nifty5/multi/block_diagonal_operator.py
+++ b/nifty5/multi/block_diagonal_operator.py
@@ -45,7 +45,7 @@ class BlockDiagonalOperator(EndomorphicOperator):
         if self._domain is not op._domain:
             raise ValueError("domain mismatch")
         res = {key : v1*v2 for key, v1, v2 in zip(self._domain.keys(), self._ops, op._ops)}
-        return BlockDiagonalOperator(res)
+        return BlockDiagonalOperator(self._domain, res)
 
     def _combine_sum(self, op, selfneg, opneg):
         from ..operators.sum_operator import SumOperator
@@ -54,4 +54,4 @@ class BlockDiagonalOperator(EndomorphicOperator):
         res = {}
         for key, v1, v2 in zip(self._domain.keys(), self._ops, op._ops):
             res[key] = SumOperator.make([v1, v2], [selfneg, opneg])
-        return BlockDiagonalOperator(res)
+        return BlockDiagonalOperator(self._domain, res)
diff --git a/test/test_multi_field.py b/test/test_multi_field.py
index 9409b3f6a4b94950531f4fa296baeb77d13ec0bd..820d82da7a27080233414ee0030c8de6ceb9fc3b 100644
--- a/test/test_multi_field.py
+++ b/test/test_multi_field.py
@@ -39,8 +39,8 @@ class Test_Functionality(unittest.TestCase):
             assert_equal(val.local_data, f2[key].local_data)
 
     def test_blockdiagonal(self):
-        op = ift.BlockDiagonalOperator({"d1":
-                                        ift.ScalingOperator(20., dom["d1"])})
+        op = ift.BlockDiagonalOperator(
+            dom, {"d1": ift.ScalingOperator(20., dom["d1"])})
         op2 = op*op
         ift.extra.consistency_check(op2)
         assert_equal(type(op2), ift.BlockDiagonalOperator)