diff --git a/builtins/2.7/datetime.pyi b/builtins/2.7/datetime.pyi
index 62d451c01..28ee105d7 100644
--- a/builtins/2.7/datetime.pyi
+++ b/builtins/2.7/datetime.pyi
@@ -47,7 +47,7 @@ class date(object):
 
     def ctime(self) -> str: ...
     def strftime(self, fmt: str) -> str: ...
-    def __format__(self, fmt: str) -> str: ...
+    def __format__(self, fmt: Union[str, unicode]) -> str: ...
     def isoformat(self) -> str: ...
     def timetuple(self) -> tuple: ... # TODO return type
     def toordinal(self) -> int: ...
@@ -190,7 +190,8 @@ class datetime(object):
     def toordinal(self) -> int: ...
     def timetuple(self) -> tuple: ... # TODO return type
     def timestamp(self) -> float: ...
-    def utctimetuple(self) -> tuple: ... # TODO return type
+    def utctimetuple(self) -> tuple: # TODO return type
+        raise OverflowError()
     def date(self) -> _date: ...
     def time(self) -> _time: ...
     def timetz(self) -> _time: ...