diff --git a/src/crypto/tls/common.go b/src/crypto/tls/common.go
index 7d686fd..f860ac9 100644
--- a/src/crypto/tls/common.go
+++ b/src/crypto/tls/common.go
@@ -1338,7 +1338,7 @@
 		return nil
 	}
 
-	logLine := []byte(fmt.Sprintf("%s %x %x\n", label, clientRandom, secret))
+	logLine := fmt.Appendf(nil, "%s %x %x\n", label, clientRandom, secret)
 
 	writerMutex.Lock()
 	_, err := c.KeyLogWriter.Write(logLine)