diff --git a/acme/acme.go b/acme/acme.go
index 02fde12..6e6c9d1 100644
--- a/acme/acme.go
+++ b/acme/acme.go
@@ -55,8 +55,9 @@
 	ALPNProto = "acme-tls/1"
 )
 
-// idPeACMEIdentifierV1 is the OID for the ACME extension for the TLS-ALPN challenge.
-var idPeACMEIdentifierV1 = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 30, 1}
+// idPeACMEIdentifier is the OID for the ACME extension for the TLS-ALPN challenge.
+// https://tools.ietf.org/html/draft-ietf-acme-tls-alpn-05#section-5.1
+var idPeACMEIdentifier = asn1.ObjectIdentifier{1, 3, 6, 1, 5, 5, 7, 1, 31}
 
 const (
 	maxChainLen = 5       // max depth and breadth of a certificate chain
@@ -778,7 +779,7 @@
 		return tls.Certificate{}, err
 	}
 	acmeExtension := pkix.Extension{
-		Id:       idPeACMEIdentifierV1,
+		Id:       idPeACMEIdentifier,
 		Critical: true,
 		Value:    extValue,
 	}
diff --git a/acme/acme_test.go b/acme/acme_test.go
index 8d94dd6..e2f446f 100644
--- a/acme/acme_test.go
+++ b/acme/acme_test.go
@@ -1317,7 +1317,7 @@
 	}
 	acmeExts := []pkix.Extension{}
 	for _, ext := range cert.Extensions {
-		if idPeACMEIdentifierV1.Equal(ext.Id) {
+		if idPeACMEIdentifier.Equal(ext.Id) {
 			acmeExts = append(acmeExts, ext)
 		}
 	}