diff --git a/pyproject.toml b/pyproject.toml
index b705cbb..ebf5590 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -66,4 +66,11 @@ omit = [
 line_length = 119
 multi_line_output = 5
 include_trailing_comma = true
-known_first_party = ["conllu", "tests"]
\ No newline at end of file
+known_first_party = ["conllu", "tests"]
+
+[tool.mypy]
+check_untyped_defs = true
+exclude = [
+    'tests',
+    'build',
+]
\ No newline at end of file