diff --git a/src/core/obj.js b/src/core/obj.js
index 0762adce8..98e7a1722 100644
--- a/src/core/obj.js
+++ b/src/core/obj.js
@@ -220,7 +220,13 @@ var Ref = (function RefClosure() {
 
   Ref.prototype = {
     toString: function Ref_toString() {
-      return 'R' + this.num + '.' + this.gen;
+      // This function is hot, so we make the string as compact as possible.
+      // |this.gen| is almost always zero, so we treat that case specially.
+      var str = this.num + 'R';
+      if (this.gen !== 0) {
+        str += this.gen;
+      }
+      return str;
     }
   };