diff --git a/conn.go b/conn.go
index 30707e0..73267f9 100644
--- a/conn.go
+++ b/conn.go
@@ -1645,9 +1645,9 @@ func (c *Conn) handshakeContext(ctx context.Context) (ret error) {
 			// the handshake (RFC 9001, Section 5.7).
 			c.quicSetReadSecret(QUICEncryptionLevelApplication, c.cipherSuite, c.in.trafficSecret)
 		} else {
-			var a alert
 			c.out.Lock()
-			if !errors.As(c.out.err, &a) {
+			a, ok := errors.AsType[alert](c.out.err)
+			if !ok {
 				a = alertInternalError
 			}
 			c.out.Unlock()
diff --git a/handshake_server.go b/handshake_server.go
index ad30acf..63ebfc0 100644
--- a/handshake_server.go
+++ b/handshake_server.go
@@ -948,10 +948,9 @@ func (c *Conn) processCertsFromClient(certificate Certificate) error {
 
 		chains, err := certs[0].Verify(opts)
 		if err != nil {
-			var errCertificateInvalid x509.CertificateInvalidError
-			if errors.As(err, &x509.UnknownAuthorityError{}) {
+			if _, ok := errors.AsType[x509.UnknownAuthorityError](err); ok {
 				c.sendAlert(alertUnknownCA)
-			} else if errors.As(err, &errCertificateInvalid) && errCertificateInvalid.Reason == x509.Expired {
+			} else if errCertificateInvalid, ok := errors.AsType[x509.CertificateInvalidError](err); ok && errCertificateInvalid.Reason == x509.Expired {
 				c.sendAlert(alertCertificateExpired)
 			} else {
 				c.sendAlert(alertBadCertificate)
diff --git a/quic.go b/quic.go
index 3d3693b..286afe8 100644
--- a/quic.go
+++ b/quic.go
@@ -363,12 +363,11 @@ func quicError(err error) error {
 	if err == nil {
 		return nil
 	}
-	var ae AlertError
-	if errors.As(err, &ae) {
+	if _, ok := errors.AsType[AlertError](err); ok {
 		return err
 	}
-	var a alert
-	if !errors.As(err, &a) {
+	a, ok := errors.AsType[alert](err)
+	if !ok {
 		a = alertInternalError
 	}
 	// Return an error wrapping the original error and an AlertError.