diff --git a/mypy.ini b/mypy.ini
index 3ee84ca..f83503c 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -3,5 +3,4 @@ ignore_missing_imports = true
 follow_imports = error
 warn_no_return = true
 warn_redundant_casts = true
-# TODO: disallow untyped defs once we have full type hint coverage
-disallow_untyped_defs = false
+disallow_untyped_defs = true