diff --git a/src/cmd/go/internal/modfetch/repo.go b/src/cmd/go/internal/modfetch/repo.go
index 20469c5432..0bffa55af6 100644
--- a/src/cmd/go/internal/modfetch/repo.go
+++ b/src/cmd/go/internal/modfetch/repo.go
@@ -183,7 +183,8 @@ type lookupCacheKey struct {
 // from its origin, and "noproxy" indicates that the patch should be fetched
 // directly only if GONOPROXY matches the given path.
 //
-// For the distinguished proxy "off", Lookup always returns a non-nil error.
+// For the distinguished proxy "off", Lookup always returns a Repo that returns
+// a non-nil error for every method call.
 //
 // A successful return does not guarantee that the module
 // has any defined versions.