diff --git a/nifty/operators/composed_operator/composed_operator.py b/nifty/operators/composed_operator/composed_operator.py
index 66d1a74493541023d274af44c55bb036f4fa6cd8..adb800032a80ecdb8082a6cc5e6d125bed88a2f2 100644
--- a/nifty/operators/composed_operator/composed_operator.py
+++ b/nifty/operators/composed_operator/composed_operator.py
@@ -96,6 +96,8 @@ class ComposedOperator(LinearOperator):
         is not easily forecasteable what the output of an operator-call
         will look like.
         """
+        if spaces is None:
+            spaces = self.default_spaces
         return spaces
 
     # ---Mandatory properties and methods---