diff --git a/.mypy.ini b/.mypy.ini
index 38afbb67..10ef53b7 100644
--- a/.mypy.ini
+++ b/.mypy.ini
@@ -5,5 +5,5 @@ scripts_are_modules = True
 ; Without this bare `mypy <file>` may get warnings for e.g.
 ;   `<var> = <value>`
 ; i.e. no typing info.
-check-untyped-defs = True
+check_untyped_defs = True
 ; platform = darwin