diff --git a/lib/Edge.ts b/lib/Edge.ts
index 2ba92ca..638b293 100644
--- a/lib/Edge.ts
+++ b/lib/Edge.ts
@@ -6,10 +6,12 @@ export class Edge {
   public target: string;
   public style?: EdgeStyles;
   public color?: Color;
+  private _directional: boolean;
 
-  public constructor (origin: string, target: string) {
+  public constructor (origin: string, target: string, directional: boolean) {
     this.origin = origin;
     this.target = target;
+    this._directional = directional;
   }
 
   // eslint-disable-next-line @typescript-eslint/naming-convention
@@ -23,7 +25,9 @@ export class Edge {
     const attr_string = ` [${attributes.map ((v) => `${v.name}="${v.value}"`)
       .join (',')}]`;
 
-    return `${this.origin} -> ${this.target}${attributes.length > 0
+    return `${this.origin} -${
+      this._directional ? '>' : '-'
+    } ${this.target}${attributes.length > 0
       ? attr_string
       : ''}`;
   }
diff --git a/lib/Graph.ts b/lib/Graph.ts
index 6582c77..43707e8 100644
--- a/lib/Graph.ts
+++ b/lib/Graph.ts
@@ -18,12 +18,13 @@ export class Graph extends Element {
   public edges: Array<Edge> = [];
   public style?: GraphStyles;
   public color?: Color;
+  public directional = true;
 
   // eslint-disable-next-line @typescript-eslint/naming-convention
   public toString (): string {
     const header = this.parent
       ? `subgraph cluster_${this.full_name}`
-      : `digraph ${this.full_name}`;
+      : `${this.directional ? 'di' : ''}graph ${this.full_name}`;
     const attributes = [];
     if (this.color)
       attributes.push ({ name: 'color', value: this.color.toString () });
@@ -85,6 +86,6 @@ export class Graph extends Element {
   }
 
   public add_edge (origin: string, target: string): void {
-    this.edges.push (new Edge (origin, target));
+    this.edges.push (new Edge (origin, target, this.directional));
   }
 }
diff --git a/test/Edge.ts b/test/Edge.ts
index 9cd51c9..0daa371 100644
--- a/test/Edge.ts
+++ b/test/Edge.ts
@@ -2,7 +2,15 @@ import test from 'ava';
 import { Edge, Color, EdgeStyles } from '../lib';
 
 test ('serialize', (t) => {
-  const e = new Edge ('foo', 'bar');
+  const e = new Edge ('foo', 'bar', false);
+  e.color = Color.white;
+  e.style = EdgeStyles.dashed;
+  const serialized = e.toString ();
+  t.is (serialized, 'foo -- bar [style="dashed",color="#ffffff"]');
+});
+
+test ('serialize directional', (t) => {
+  const e = new Edge ('foo', 'bar', true);
   e.color = Color.white;
   e.style = EdgeStyles.dashed;
   const serialized = e.toString ();