diff --git a/marray/__init__.py b/marray/__init__.py
index 7e64065..5ba9fc5 100644
--- a/marray/__init__.py
+++ b/marray/__init__.py
@@ -202,7 +202,13 @@ def fun(self, name=name):
     unary_names_py = ['__bool__', '__complex__', '__float__', '__index__', '__int__']
     for name in unary_names_py:
         def fun(self, name=name):
-            return self._call_super_method(name)
+            res = self._call_super_method(name)
+            if res and not self.mask:
+                return res
+            if name in {'__complex__', '__float__'}:
+                return res * mod.nan
+            raise ValueError(f"Cannot convert masked value to `{name.strip('_')}`.")
+
         setattr(MArray, name, fun)
 
     # Methods that return the result of an elementwise binary operation
diff --git a/marray/tests/test_marray.py b/marray/tests/test_marray.py
index 4374338..6233ca2 100644
--- a/marray/tests/test_marray.py
+++ b/marray/tests/test_marray.py
@@ -319,7 +319,7 @@ def test_indexing(xp):
     assert isinstance(x[1], type(x))
 
     # Test `__setitem__`/`__getitem__` roundtrip with masked array as index
-    i = mxp.asarray(1, mask=True)
+    i = mxp.asarray(1, mask=False)
     x[i.__index__()] = 20
     assert x[i.__index__()] == 20
     assert isinstance(x[i.__index__()], type(x))