diff --git a/index.js b/index.js
index 77668e0..6ea05f1 100644
--- a/index.js
+++ b/index.js
@@ -1,28 +1,53 @@
-exports.encode = exports.stringify = function (value) {
-  var values = [value];
+function encode(value) {
+  return JSON.stringify(tabulate(value));
+}
+
+function tabulate(value) {
+  var values = [];
   var table = [];
+  var indexMap = typeof Map === "function" && new Map;
+
+  function getIndex(value) {
+    var index;
+
+    if (indexMap) {
+      // If we have Map, use it instead of values.indexOf to accelerate
+      // object lookups.
+      index = indexMap.get(value);
+      if (typeof index === "undefined") {
+        index = values.push(value) - 1;
+        indexMap.set(value, index);
+      }
+    } else {
+      index = values.indexOf(value);
+      if (index < 0) {
+        index = values.push(value) - 1;
+      }
+    }
+
+    return index;
+  }
+
+  // Assign the root value to values[0].
+  getIndex(value);
 
   for (var v = 0; v < values.length; ++v) {
     value = values[v];
+
     if (value && typeof value === "object") {
       var copy = table[v] = Array.isArray(value) ? [] : {};
       Object.keys(value).forEach(function (key) {
-        var child = value[key];
-        var index = values.indexOf(child);
-        if (index < 0) {
-          index = values.push(child) - 1;
-        }
-        copy[key] = index;
+        copy[key] = getIndex(value[key]);
       });
     } else {
       table[v] = value;
     }
   }
 
-  return JSON.stringify(table);
-};
+  return table;
+}
 
-exports.decode = exports.parse = function (encoding) {
+function decode(encoding) {
   var table = JSON.parse(encoding);
 
   table.forEach(function (entry) {
@@ -34,4 +59,7 @@ exports.decode = exports.parse = function (encoding) {
   });
 
   return table[0];
-};
+}
+
+exports.encode = exports.stringify = encode;
+exports.decode = exports.parse = decode;