diff --git a/torba/basetransaction.py b/torba/basetransaction.py
index 20935ba3c..9c653b825 100644
--- a/torba/basetransaction.py
+++ b/torba/basetransaction.py
@@ -138,7 +138,7 @@ class BaseInput(InputOutput):
         return self.txo_ref.txo.amount
 
     @property
-    def is_my_account(self) -> int:
+    def is_my_account(self) -> Optional[bool]:
         """ True if the output this input spends is yours. """
         if self.txo_ref.txo is None:
             raise ValueError('Cannot resolve output to determine ownership.')
@@ -237,8 +237,8 @@ class BaseTransaction:
     input_class = BaseInput
     output_class = BaseOutput
 
-    def __init__(self, raw=None, version: int=1, locktime: int=0,
-                 height: int=-1, position: int=-1) -> None:
+    def __init__(self, raw=None, version: int = 1, locktime: int = 0,
+                 height: int = -1, position: int = -1) -> None:
         self._raw = raw
         self.ref = TXRefMutable(self)
         self.version = version