diff --git a/lib/util.js b/lib/util.js
index 8de905f4dc..c7fcbccc8a 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -33,12 +33,12 @@ exports.format = function(f) {
   var args = arguments;
   var len = args.length;
   var str = String(f).replace(formatRegExp, function(x) {
+    if (x === '%%') return '%';
     if (i >= len) return x;
     switch (x) {
       case '%s': return String(args[i++]);
       case '%d': return Number(args[i++]);
       case '%j': return JSON.stringify(args[i++]);
-      case '%%': return '%';
       default:
         return x;
     }
diff --git a/test/simple/test-util-format.js b/test/simple/test-util-format.js
index 83238f9815..b5592203a3 100644
--- a/test/simple/test-util-format.js
+++ b/test/simple/test-util-format.js
@@ -58,4 +58,5 @@ assert.equal(util.format('%s:%s', undefined), 'undefined:%s');
 assert.equal(util.format('%s:%s', 'foo'), 'foo:%s');
 assert.equal(util.format('%s:%s', 'foo', 'bar'), 'foo:bar');
 assert.equal(util.format('%s:%s', 'foo', 'bar', 'baz'), 'foo:bar baz');
-
+assert.equal(util.format('%%%s%%', 'hi'), '%hi%');
+assert.equal(util.format('%%%s%%%%', 'hi'), '%hi%%');