diff --git a/mockgen/tests/vendor_dep/doc.go b/mockgen/tests/vendor_dep/doc.go
index <HASH>..<HASH> 100644
--- a/mockgen/tests/vendor_dep/doc.go
+++ b/mockgen/tests/vendor_dep/doc.go
@@ -1,3 +1,4 @@
 package vendor_dep
 
 //go:generate mockgen -package vendor_dep -destination mock.go github.com/golang/mock/mockgen/tests/vendor_dep VendorsDep
+//go:generate mockgen -destination source_mock_package/mock.go -source=vendor_dep.go
Add a (failing) test case for using source mode to mock something that depends on a vendored package.