diff --git a/cmd/sendmail/main.go b/cmd/sendmail/main.go
index 5d7dc84..df894b3 100644
--- a/cmd/sendmail/main.go
+++ b/cmd/sendmail/main.go
@@ -52,7 +52,7 @@ func (a *plainClient) Start(si *smtp.ServerInfo) (mech string, ir []byte, err er
 }
 
 func (a *plainClient) Next(challenge []byte, b bool) (response []byte, err error) {
-	slog.Info("Next: %v", challenge)
+	slog.Info("Next: %v", slog.String("challenge", string(challenge)))
 	return nil, nil
 }