diff --git a/lib/_debugger.js b/lib/_debugger.js
index 9e1c5844cd7..3e28a3f4cb6 100644
--- a/lib/_debugger.js
+++ b/lib/_debugger.js
@@ -922,13 +922,17 @@ function intChars(n) {
 
 // Adds spaces and prefix to number
 function leftPad(n, prefix) {
-  var s = n.toString();
-  var nchars = intChars(n);
-  var nspaces = nchars - s.length;
+  var s = n.toString(),
+      nchars = intChars(n),
+      nspaces = nchars - s.length - 1;
+
+  prefix || (prefix = ' ');
+
   for (var i = 0; i < nspaces; i++) {
-    s = (prefix || ' ') + s;
+    prefix += ' ';
   }
-  return s;
+
+  return prefix + s;
 }