diff --git a/lib/log.js b/lib/log.js
index 394b356c..b74feb03 100644
--- a/lib/log.js
+++ b/lib/log.js
@@ -52,7 +52,7 @@ log.init = function() {
       const args = Array.from(arguments);
       if (name !== 'INFO') args.unshift('[' + name + ']');
 
-      let s = args.map(x => x.toString()).join(' ');
+      let s = args.map(x => ('' + x.toString())).join(' ');
       if (level.color) s = chalk[level.color](s);
 
       this.output(s);