diff --git a/boringproxy.go b/boringproxy.go
index 06deff4..ced3224 100644
--- a/boringproxy.go
+++ b/boringproxy.go
@@ -57,6 +57,7 @@ func Listen() {
 	acmeEmail := flagSet.String("acme-email", "", "Email for ACME (ie Let's Encrypt)")
 	acmeUseStaging := flagSet.Bool("acme-use-staging", false, "Use ACME (ie Let's Encrypt) staging servers")
 	acceptCATerms := flagSet.Bool("accept-ca-terms", false, "Automatically accept CA terms")
+	acmeCa := flagSet.String("acme-certificate-authority", "", "URI for ACME Certificate Authority")
 	err := flagSet.Parse(os.Args[2:])
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%s: parsing flags: %s\n", os.Args[0], err)
@@ -117,6 +118,10 @@ func Listen() {
 		certmagic.DefaultACME.CA = certmagic.LetsEncryptStagingCA
 	}
 
+	if *acmeCa != "" {
+		certmagic.DefaultACME.CA = *acmeCa
+	}
+
 	certConfig := certmagic.NewDefault()
 
 	if *newAdminDomain != "" {