diff --git a/tools/clean-repos/main.go b/tools/clean-repos/main.go
index 235ca9e..6739191 100644
--- a/tools/clean-repos/main.go
+++ b/tools/clean-repos/main.go
@@ -1,13 +1,17 @@
 package main
 
 import (
+	"flag"
 	"io/ioutil"
 	"log"
 	"os"
 	"time"
 )
 
+var real = flag.Bool("real", false, "run the deletions")
+
 func main() {
+	flag.Parse()
 	files, err := ioutil.ReadDir("_repos/src")
 	if err != nil {
 		log.Fatal(err)
@@ -22,8 +26,12 @@ func main() {
 			for _, d := range dirs {
 				if time.Now().Sub(d.ModTime()) > 30*24*time.Hour {
 					path := "_repos/src/" + f.Name() + "/" + d.Name()
-					log.Printf("Deleting %s...", path)
-					os.RemoveAll(path)
+					if *real {
+						log.Printf("Deleting %s...", path)
+						os.RemoveAll(path)
+					} else {
+						log.Printf("Would delete %s", path)
+					}
 				}
 			}
 		}