diff --git a/config.go b/config.go
index 12fc124..dee054e 100644
--- a/config.go
+++ b/config.go
@@ -3,6 +3,7 @@ package main
 import (
 	"log"
 	"os"
+	"sync"
 	"time"
 
 	"github.com/gorhill/cronexpr"
@@ -19,12 +20,13 @@ const (
 )
 
 type Repo struct {
-	URL                  string    `yaml:"url"`
-	URLs                 []string  `yaml:"urls"`
-	Mirrorlist           string    `yaml:"mirrorlist"`
-	HttpProxy            string    `yaml:"http_proxy"`
-	LastMirrorlistCheck  time.Time `yaml:"-"`
-	LastModificationTime time.Time `yaml:"-"`
+	URL                  string     `yaml:"url"`
+	URLs                 []string   `yaml:"urls"`
+	Mirrorlist           string     `yaml:"mirrorlist"`
+	HttpProxy            string     `yaml:"http_proxy"`
+	LastMirrorlistCheck  time.Time  `yaml:"-"`
+	MirrorlistMutex      sync.Mutex `yaml:"-"`
+	LastModificationTime time.Time  `yaml:"-"`
 }
 
 type RefreshPeriod struct {
diff --git a/downloader.go b/downloader.go
index b22b1d0..a5ee38a 100644
--- a/downloader.go
+++ b/downloader.go
@@ -59,7 +59,8 @@ func (d *Downloader) decrementUsage() {
 }
 
 func (d *Downloader) download() error {
-	if len(d.repo.getUrls()) == 0 {
+	urls := d.repo.getUrls()
+	if len(urls) == 0 {
 		return fmt.Errorf("repo %v has no urls", d.repoName)
 	}
 
@@ -70,7 +71,7 @@ func (d *Downloader) download() error {
 		proxyURL = nil
 	}
 
-	for _, u := range d.repo.getUrls() {
+	for _, u := range urls {
 		err := d.downloadFromUpstream(u, proxyURL)
 		if err != nil {
 			log.Printf("unable to download file %v: %v", d.key, err)
diff --git a/urls.go b/urls.go
index 1ebaab8..39c531f 100644
--- a/urls.go
+++ b/urls.go
@@ -44,11 +44,23 @@ func parseMirrorlistURLs(file *os.File) ([]string, error) {
 }
 
 func (r *Repo) getMirrorlistURLs() ([]string, error) {
-	if time.Since(r.LastMirrorlistCheck) < 5*time.Second {
+	const MirrorlistCheckInterval = 5*time.Second
+
+	if time.Since(r.LastMirrorlistCheck) < MirrorlistCheckInterval {
+		return r.URLs, nil
+	}
+
+	r.MirrorlistMutex.Lock()
+	defer r.MirrorlistMutex.Unlock()
+
+	// Test time again in case another routine already checked in the meantime
+	if time.Since(r.LastMirrorlistCheck) < MirrorlistCheckInterval {
 		return r.URLs, nil
 	}
 
-	r.LastMirrorlistCheck = time.Now()
+	defer func() {
+		r.LastMirrorlistCheck = time.Now()
+	}()
 
 	fileInfo, err := os.Stat(r.Mirrorlist)
 	if err != nil {