diff --git a/cmd/vet/types.go b/cmd/vet/types.go
index 5c9fc89a..45c20b03 100644
--- a/cmd/vet/types.go
+++ b/cmd/vet/types.go
@@ -20,10 +20,17 @@ var imports = make(map[string]*types.Package)
 var (
 	stringerMethodType = types.New("func() string")
 	errorType          = types.New("error").Underlying().(*types.Interface)
-	stringerType       = importType("fmt", "Stringer").Underlying().(*types.Interface)
-	formatterType      = importType("fmt", "Formatter").Underlying().(*types.Interface)
+	stringerType       = types.New("interface{ String() string }").(*types.Interface)
+	formatterType      *types.Interface
 )
 
+func init() {
+	typ := importType("fmt", "Formatter")
+	if typ != nil {
+		formatterType = typ.Underlying().(*types.Interface)
+	}
+}
+
 // importType returns the type denoted by the qualified identifier
 // path.name, and adds the respective package to the imports map
 // as a side effect.