diff --git a/lib/graph.ex b/lib/graph.ex
index 679ede0..d7ad493 100644
--- a/lib/graph.ex
+++ b/lib/graph.ex
@@ -693,7 +693,7 @@ defmodule Graph do
     end
   end
 
-  def add_vertex(g, v, label) do
+  def add_vertex(%__MODULE__{} = g, v, label) when not is_list(label) do
     add_vertex(g, v, [label])
   end