diff --git a/stdlib/2/__builtin__.pyi b/stdlib/2/__builtin__.pyi
index 2ef4c0e0c..97722e453 100644
--- a/stdlib/2/__builtin__.pyi
+++ b/stdlib/2/__builtin__.pyi
@@ -33,7 +33,7 @@ class _SupportsIndex(Protocol):
     def __index__(self) -> int: ...
 
 class _SupportsLessThan(Protocol):
-    def __lt__(self, other: Any) -> bool: ...
+    def __lt__(self, __other: Any) -> bool: ...
 
 _T = TypeVar('_T')
 _T_co = TypeVar('_T_co', covariant=True)
diff --git a/stdlib/2and3/builtins.pyi b/stdlib/2and3/builtins.pyi
index 2ef4c0e0c..97722e453 100644
--- a/stdlib/2and3/builtins.pyi
+++ b/stdlib/2and3/builtins.pyi
@@ -33,7 +33,7 @@ class _SupportsIndex(Protocol):
     def __index__(self) -> int: ...
 
 class _SupportsLessThan(Protocol):
-    def __lt__(self, other: Any) -> bool: ...
+    def __lt__(self, __other: Any) -> bool: ...
 
 _T = TypeVar('_T')
 _T_co = TypeVar('_T_co', covariant=True)