diff --git a/monitor/discoveredcert.go b/monitor/discoveredcert.go
index a5b4055..47fec9b 100644
--- a/monitor/discoveredcert.go
+++ b/monitor/discoveredcert.go
@@ -42,7 +42,7 @@ type certPaths struct {
 func (cert *DiscoveredCert) pemChain() []byte {
 	var buffer bytes.Buffer
 	if cert.ChainError != nil {
-		fmt.Fprintln(&buffer, "Warning: this chain may be incomplete or invalid: %s", cert.ChainError)
+		fmt.Fprintln(&buffer, "Warning: this chain may be incomplete or invalid: ", cert.ChainError)
 	}
 	for _, certBytes := range cert.Chain {
 		if err := pem.Encode(&buffer, &pem.Block{