diff --git a/internal/cert/cert.go b/internal/cert/cert.go
index af69067..0d66ada 100644
--- a/internal/cert/cert.go
+++ b/internal/cert/cert.go
@@ -76,7 +76,9 @@ func CollectMetrics(ctx context.Context, path string, cfg Config) (Metrics, erro
 	if err != nil {
 		return metrics, err
 	}
-	metrics.Tags = map[string]string{"subject": cert.Subject.CommonName}
+	fixStar := strings.Replace(cert.Subject.CommonName, "*", "STAR", 1)
+	fixDot := strings.ReplaceAll(fixStar, ".", "_")
+	metrics.Tags = map[string]string{"subject": fixDot}
 	if cfg.ServerName != "" {
 		if err := cert.VerifyHostname(cfg.ServerName); err != nil {
 			return metrics, fmt.Errorf("error supplied servername not valid for this certificate: %v", err)