diff --git a/hamilton.go b/hamilton.go
index 3e2cb78..a4147db 100644
--- a/hamilton.go
+++ b/hamilton.go
@@ -31,6 +31,7 @@ var step int
 func writeGraphfile(g [][]int, path []int) {
 	filename := fmt.Sprintf("step%07d.dot", step)
 	f, _ := os.Create(filename)
+	defer f.Close()
 	step++
 	fmt.Fprintln(f, "digraph {")
 	fmt.Fprintln(f, "dpi=200")