diff --git a/lib/common.js b/lib/common.js
index 2a5eaaa..b7a6750 100755
--- a/lib/common.js
+++ b/lib/common.js
@@ -192,8 +192,8 @@ function humanDurationFromMs(ms) {
  */
 function humanSizeFromBytes(opts, bytes) {
     if (bytes === undefined) {
-        opts = {};
         bytes = opts;
+        opts = {};
     }
     assert.number(bytes, 'bytes');
     // The number of decimal places, default 1.
diff --git a/test/unit/common.test.js b/test/unit/common.test.js
index de25107..096c377 100644
--- a/test/unit/common.test.js
+++ b/test/unit/common.test.js
@@ -35,6 +35,16 @@ test('humanDurationFromMs', function (t) {
 
     t.equal(humanDurationFromMs(47*second), '47s');
     t.equal(humanDurationFromMs(1*week), '1w');
+    t.equal(humanDurationFromMs(0), '0ms');
+
+    t.end();
+});
+
+test('humanSizeFromBytes', function (t) {
+    var humanSizeFromBytes = common.humanSizeFromBytes;
+
+    t.equal(humanSizeFromBytes(0), '0 B');
+    t.equal(humanSizeFromBytes({}, 0), '0 B');
 
     t.end();
 });