diff --git a/src/models/append_graph.rs b/src/models/append_graph.rs
index 9ccfef7..2487f23 100644
--- a/src/models/append_graph.rs
+++ b/src/models/append_graph.rs
@@ -91,7 +91,7 @@ impl GraphTopology for AppendGraph {
     }
 
     fn vertex_capacity(&self) -> usize {
-        self.vertices.len()
+        self.vertices.capacity()
     }
 
     fn vertex_map<T: Clone>(&self, default: T) -> VertexMap<Self::Vertex, T> {