diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..4edbd63
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "vendor/screw_unit"]
+	path = vendor/screw_unit
+	url = git://github.com/nathansobo/screw-unit.git
diff --git a/vendor/screw_unit b/vendor/screw_unit
new file mode 160000
index 0000000..dc60a3e
--- /dev/null
+++ b/vendor/screw_unit
@@ -0,0 +1 @@
+Subproject commit dc60a3e625f3cae262995faa4296a98104a62f0f