diff --git a/.mypy.ini b/.mypy.ini
index f9ec5997..38afbb67 100644
--- a/.mypy.ini
+++ b/.mypy.ini
@@ -2,4 +2,8 @@
 follow_imports = skip
 ignore_missing_imports = True
 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
 ; platform = darwin