diff --git a/client.go b/client.go
index d534fbe..b194c40 100644
--- a/client.go
+++ b/client.go
@@ -4,7 +4,6 @@ import (
 	"context"
 	"crypto/tls"
 	"crypto/x509"
-	"errors"
 	"net"
 	"net/url"
 	"time"
@@ -183,7 +182,7 @@ func (c *Client) verifyConnection(cs tls.ConnectionState, hostname string) error
 	}
 	// Check expiration date
 	if !time.Now().Before(cert.NotAfter) {
-		return errors.New("gemini: certificate expired")
+		return ErrCertificateExpired
 	}
 	// See if the client trusts the certificate
 	if c.TrustCertificate != nil {
diff --git a/gemini.go b/gemini.go
index 6b419cc..9e6c653 100644
--- a/gemini.go
+++ b/gemini.go
@@ -11,6 +11,8 @@ var (
 	ErrInvalidRequest  = errors.New("gemini: invalid request")
 	ErrInvalidResponse = errors.New("gemini: invalid response")
 
+	ErrCertificateExpired = errors.New("gemini: certificate expired")
+
 	// ErrBodyNotAllowed is returned by ResponseWriter.Write calls
 	// when the response status code does not permit a body.
 	ErrBodyNotAllowed = errors.New("gemini: response status code does not allow body")