diff --git a/jwk/rsa.go b/jwk/rsa.go
index f8a365ed9..5ef2260c4 100644
--- a/jwk/rsa.go
+++ b/jwk/rsa.go
@@ -26,7 +26,7 @@ func (k *rsaPrivateKey) FromRaw(rawKey *rsa.PrivateKey) error {
 	l := len(rawKey.Primes)
 
 	if l < 0 /* I know, I'm being paranoid */ || l > 2 {
-		return fmt.Errorf(`invalid number of primes in rsa.PrivateKey: need 1 or 2, got %d`, len(rawKey.Primes))
+		return fmt.Errorf(`invalid number of primes in rsa.PrivateKey: need 0 to 2, but got %d`, len(rawKey.Primes))
 	}
 
 	if l > 0 {