diff --git a/2021/day01/go.mod b/2021/day01/go.mod
new file mode 100644
index 0000000..2a8c064
--- /dev/null
+++ b/2021/day01/go.mod
@@ -0,0 +1,3 @@
+module 2021/day01
+
+go 1.25.4