diff --git a/Package.swift b/Package.swift
index 29ccaf8..c8d16f2 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,3 +1,6 @@
+// swift-tools-version:5.1
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
 import PackageDescription
 
 let package = Package(