diff --git a/provider/github-app-token/github/jwk/jwk.go b/provider/github-app-token/github/jwk/jwk.go
index 07249ba5..a31b70a3 100644
--- a/provider/github-app-token/github/jwk/jwk.go
+++ b/provider/github-app-token/github/jwk/jwk.go
@@ -125,7 +125,7 @@ func (key *commonKey) PublicKey() interface{} {
 
 func (key *commonKey) decode() error {
 	// decode the certificates
-	certs := make([]*x509.Certificate, len(key.X5c))
+	certs := make([]*x509.Certificate, 0, len(key.X5c))
 	for _, der := range key.X5c {
 		cert, err := x509.ParseCertificate(der)
 		if err != nil {
diff --git a/provider/github-app-token/github/jwk/jwk_test.go b/provider/github-app-token/github/jwk/jwk_test.go
index a995f6d7..4dcbb6fd 100644
--- a/provider/github-app-token/github/jwk/jwk_test.go
+++ b/provider/github-app-token/github/jwk/jwk_test.go
@@ -207,3 +207,59 @@ func TestKeyAppendixA(t *testing.T) {
 		}
 	})
 }
+
+func TestKeyAppendixB(t *testing.T) {
+	// RFC7517 Appendix B. Example Use of "x5c" (X.509 Certificate Chain) Parameter
+	rawKey := ` {"kty":"RSA",` +
+		`"use":"sig",` +
+		`"kid":"1b94c",` +
+		`"n":"vrjOfz9Ccdgx5nQudyhdoR17V-IubWMeOZCwX_jj0hgAsz2J_pqYW08` +
+		`PLbK_PdiVGKPrqzmDIsLI7sA25VEnHU1uCLNwBuUiCO11_-7dYbsr4iJmG0Q` +
+		`u2j8DsVyT1azpJC_NG84Ty5KKthuCaPod7iI7w0LK9orSMhBEwwZDCxTWq4a` +
+		`YWAchc8t-emd9qOvWtVMDC2BXksRngh6X5bUYLy6AyHKvj-nUy1wgzjYQDwH` +
+		`MTplCoLtU-o-8SNnZ1tmRoGE9uJkBLdh5gFENabWnU5m1ZqZPdwS-qo-meMv` +
+		`VfJb6jJVWRpl2SUtCnYG2C32qvbWbjZ_jBPD5eunqsIo1vQ",` +
+		`"e":"AQAB",` +
+		`"x5c":` +
+		`["MIIDQjCCAiqgAwIBAgIGATz/FuLiMA0GCSqGSIb3DQEBBQUAMGIxCzAJB` +
+		`gNVBAYTAlVTMQswCQYDVQQIEwJDTzEPMA0GA1UEBxMGRGVudmVyMRwwGgYD` +
+		`VQQKExNQaW5nIElkZW50aXR5IENvcnAuMRcwFQYDVQQDEw5CcmlhbiBDYW1` +
+		`wYmVsbDAeFw0xMzAyMjEyMzI5MTVaFw0xODA4MTQyMjI5MTVaMGIxCzAJBg` +
+		`NVBAYTAlVTMQswCQYDVQQIEwJDTzEPMA0GA1UEBxMGRGVudmVyMRwwGgYDV` +
+		`QQKExNQaW5nIElkZW50aXR5IENvcnAuMRcwFQYDVQQDEw5CcmlhbiBDYW1w` +
+		`YmVsbDCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAL64zn8/QnH` +
+		`YMeZ0LncoXaEde1fiLm1jHjmQsF/449IYALM9if6amFtPDy2yvz3YlRij66` +
+		`s5gyLCyO7ANuVRJx1NbgizcAblIgjtdf/u3WG7K+IiZhtELto/A7Fck9Ws6` +
+		`SQvzRvOE8uSirYbgmj6He4iO8NCyvaK0jIQRMMGQwsU1quGmFgHIXPLfnpn` +
+		`fajr1rVTAwtgV5LEZ4Iel+W1GC8ugMhyr4/p1MtcIM42EA8BzE6ZQqC7VPq` +
+		`PvEjZ2dbZkaBhPbiZAS3YeYBRDWm1p1OZtWamT3cEvqqPpnjL1XyW+oyVVk` +
+		`aZdklLQp2Btgt9qr21m42f4wTw+Xrp6rCKNb0CAwEAATANBgkqhkiG9w0BA` +
+		`QUFAAOCAQEAh8zGlfSlcI0o3rYDPBB07aXNswb4ECNIKG0CETTUxmXl9KUL` +
+		`+9gGlqCz5iWLOgWsnrcKcY0vXPG9J1r9AqBNTqNgHq2G03X09266X5CpOe1` +
+		`zFo+Owb1zxtp3PehFdfQJ610CDLEaS9V9Rqp17hCyybEpOGVwe8fnk+fbEL` +
+		`2Bo3UPGrpsHzUoaGpDftmWssZkhpBJKVMJyf/RuP2SmmaIzmnw9JiSlYhzo` +
+		`4tpzd5rFXhjRbg4zW9C+2qok+2+qDM1iJ684gPHMIY8aLWrdgQTxkumGmTq` +
+		`gawR+N5MDtdPTEQ0XfIBc2cJEUyMTY5MPvACWpkA6SdS4xSvdXK3IVfOWA=="]` +
+		`}`
+	key, err := ParseKey([]byte(rawKey))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if key.KeyType() != "RSA" {
+		t.Errorf("unexpected key type: want %s, got %s", "RSA", key.KeyType())
+	}
+	if len(key.X509CertificateChain()) != 1 {
+		t.Errorf("unexpected certificate chain length: want 1, got %d", len(key.X509CertificateChain()))
+	}
+
+	keyPublicKey := key.PublicKey().(*rsa.PublicKey)
+	cert := key.X509CertificateChain()[0]
+	certPublicKey := cert.PublicKey.(*rsa.PublicKey)
+	if !keyPublicKey.Equal(certPublicKey) {
+		t.Error("public keys are missmatch")
+	}
+	issuer := "CN=Brian Campbell,O=Ping Identity Corp.,L=Denver,ST=CO,C=US"
+	if cert.Issuer.String() != issuer {
+		t.Errorf("unexpected issuer: want %q, got %q", issuer, cert.Issuer.String())
+	}
+}