diff --git a/cmd/internal/graph/common.go b/cmd/internal/graph/common.go
index 92259cf..9d242a1 100644
--- a/cmd/internal/graph/common.go
+++ b/cmd/internal/graph/common.go
@@ -23,6 +23,7 @@ import (
 
 type WeightedGraph interface {
 	graph.Weighted
+	graph.WeightedMultigraphBuilder
 
 	WeightedEdges() graph.WeightedEdges
 
diff --git a/cmd/internal/graph/dot/graph.go b/cmd/internal/graph/dot/graph.go
index 8645851..8291e76 100644
--- a/cmd/internal/graph/dot/graph.go
+++ b/cmd/internal/graph/dot/graph.go
@@ -25,19 +25,23 @@ import (
 	"gonum.org/v1/gonum/graph/multi"
 )
 
-// DOTDirectedGraph is a graph to unmarshal DOT graphs.
-type DOTDirectedGraph struct {
-	*igraph.DirectedGraph
+// DOTWeightedGraph is a graph to unmarshal DOT graphs.
+type DOTWeightedGraph struct {
+	igraph.WeightedGraph
 	WeightAttribute string
 }
 
 // NewDOTDirectedGraph returns a graph with no nodes or edges.
-func NewDOTDirectedGraph(weightAttr string) *DOTDirectedGraph {
-	return &DOTDirectedGraph{DirectedGraph: igraph.NewDirectedGraph(), WeightAttribute: weightAttr}
+func NewDOTDirectedGraph(weightAttr string) DOTWeightedGraph {
+	return DOTWeightedGraph{WeightedGraph: igraph.NewDirectedGraph(), WeightAttribute: weightAttr}
+}
+
+func NewDOTUndirectedGraph(weightAttr string) DOTWeightedGraph {
+	return DOTWeightedGraph{WeightedGraph: igraph.NewUndirectedGraph(), WeightAttribute: weightAttr}
 }
 
 // NewLine returns a DOT-aware weighted line.
-func (g *DOTDirectedGraph) NewLine(from, to graph.Node) graph.Line {
+func (g *DOTWeightedGraph) NewLine(from, to graph.Node) graph.Line {
 	var defaultWeight float64
 	if g.WeightAttribute == "" {
 		defaultWeight = 1
@@ -45,16 +49,16 @@ func (g *DOTDirectedGraph) NewLine(from, to graph.Node) graph.Line {
 		defaultWeight = math.NaN()
 	}
 
-	e := g.DirectedGraph.NewWeightedLine(from, to, defaultWeight).(multi.WeightedLine)
+	e := g.WeightedGraph.NewWeightedLine(from, to, defaultWeight).(multi.WeightedLine)
 	return &weightedLine{WeightedLine: e, weightAttribute: g.WeightAttribute}
 }
 
 // NewNode returns a DOT-aware Node.
-func (g *DOTDirectedGraph) NewNode() graph.Node {
-	return &Node{Node: g.DirectedGraph.NewNode()}
+func (g *DOTWeightedGraph) NewNode() graph.Node {
+	return &Node{Node: g.WeightedGraph.NewNode()}
 }
 
 // SetLine adds a DOT-aware weighted line to the graph.
-func (g *DOTDirectedGraph) SetLine(e graph.Line) {
-	g.DirectedGraph.SetWeightedLine(e.(*weightedLine))
+func (g *DOTWeightedGraph) SetLine(e graph.Line) {
+	g.WeightedGraph.SetWeightedLine(e.(*weightedLine))
 }