diff --git a/lambda/app/Makefile b/lambda/app/Makefile
index f3212801..bbcbe02e 100644
--- a/lambda/app/Makefile
+++ b/lambda/app/Makefile
@@ -24,7 +24,7 @@ lint-check:
 
 .PHONY: type-check
 type-check:
-	pipenv run mypy . --disallow-untyped-calls --disallow-any-generics --disallow-untyped-decorators --warn-unused-ignores
+	pipenv run mypy . --disallow-untyped-calls --disallow-any-generics --disallow-untyped-decorators --warn-unused-ignores --no-implicit-optional
 
 .PHONY: test
 test: export AWS_DEFAULT_REGION := us-east-1