diff --git a/bin/carto b/bin/carto
index 6d719f7..4ca598f 100755
--- a/bin/carto
+++ b/bin/carto
@@ -4,7 +4,7 @@ var path = require('path'),
     fs = require('fs'),
     carto = require('carto'),
     url = require('url'),
-    _ = require('lodash');
+    _ = require('underscore');
 
 var existsSync = require('fs').existsSync || require('path').existsSync
 
diff --git a/lib/carto/index.js b/lib/carto/index.js
index 64ed5b4..a0265d8 100644
--- a/lib/carto/index.js
+++ b/lib/carto/index.js
@@ -2,6 +2,7 @@ var util = require('util'),
     fs = require('fs'),
     path = require('path');
 
+
 function getVersion() {
     if (parseInt(process.version.split('.')[1], 10) > 4) {
         return require('../../package.json').version.split('.');
diff --git a/lib/carto/parser.js b/lib/carto/parser.js
index 81b1e64..f5f160d 100644
--- a/lib/carto/parser.js
+++ b/lib/carto/parser.js
@@ -3,7 +3,7 @@ var carto, tree, _;
 if (typeof(process) !== 'undefined') {
     carto = exports;
     tree = require('./tree');
-    _ = require('lodash');
+    _ = require('underscore');
 } else {
     if (typeof(window.carto) === 'undefined') { window.carto = {}; }
     carto = window.carto;
diff --git a/lib/carto/renderer.js b/lib/carto/renderer.js
index 1b16508..2fe5c9b 100644
--- a/lib/carto/renderer.js
+++ b/lib/carto/renderer.js
@@ -1,4 +1,4 @@
-var _ = require('lodash');
+var _ = require('underscore');
 var carto = require('./index');
 var tree = require('./tree');
 
@@ -29,7 +29,7 @@ carto.Renderer.prototype.render = function render(m, callback) {
     var output = [];
 
     // Transform stylesheets into rulesets.
-    var rulesets = _(m.Stylesheet)
+    var rulesets = _(m.Stylesheet).chain()
         .map(function(s) {
             if (typeof s == 'string') {
                throw new Error("Stylesheet object is expected not a string: '" + s + "'");
@@ -50,31 +50,36 @@ carto.Renderer.prototype.render = function render(m, callback) {
 
     // Iterate through layers and create styles custom-built
     // for each of them, and apply those styles to the layers.
-    m.Layer.forEach(function(l) {
+    var styles, l, classIndex, rules, sorted, matching;
+    for (var i = 0; i < m.Layer.length; i++) {
+        l = m.Layer[i];
+        styles = [];
+        classIndex = {};
+
         if (env.benchmark) console.warn('processing layer: ' + l.id);
-        l.styles = [];
         // Classes are given as space-separated alphanumeric strings.
         var classes = (l['class'] || '').split(/\s+/g);
-        var matching = rulesets.filter(function(definition) {
-            return definition.appliesTo(l.name, classes);
+        for (var j = 0; j < classes.length; j++) {
+            classIndex[classes[j]] = true;
+        }
+        matching = rulesets.filter(function(definition) {
+            return definition.appliesTo(l.name, classIndex);
         });
-        var rules = inheritRules(matching, env);
-        var sorted = sortStyles(rules, env);
+        rules = inheritRules(matching, env);
+        sorted = sortStyles(rules, env);
 
-        _(sorted).each(function(rule) {
-            var style = new tree.Style(l.name, rule.attachment, rule);
-            if (style) {
-                l.styles.push(style.name);
+        for (var k = 0, rule, style_name; k < sorted.length; k++) {
+            rule = sorted[k];
+            style_name = l.name + (rule.attachment !== '__default__' ? '-' + rule.attachment : '');
+            styles.push(style_name);
 
-                var xml = style.toXML(env);
-                // env.effects can be modified by this call
-                output.push(xml);
-            }
-        });
-        if (l.styles.length) {
-            output.push((new carto.tree.Layer(l)).toXML());
+            // env.effects can be modified by this call
+            output.push(tree.Style.toXML(style_name, rule.attachment, rule, env));
         }
-    });
+        if (styles.length) {
+            output.push(carto.tree.Layer.toXML(l, styles));
+        }
+    }
 
     output.unshift(env.effects.map(function(e) {
         return e.toXML(env);
diff --git a/lib/carto/tree/definition.js b/lib/carto/tree/definition.js
index c1a1899..9f3c2bf 100644
--- a/lib/carto/tree/definition.js
+++ b/lib/carto/tree/definition.js
@@ -11,11 +11,11 @@ tree.Definition = function Definition(selector, rules) {
     this.elements = selector.elements;
     assert.ok(selector.filters instanceof tree.Filterset);
     this.rules = rules;
-    this.ruleIndex = [];
+    this.ruleIndex = {};
     for (var i = 0; i < this.rules.length; i++) {
         if ('zoom' in this.rules[i]) this.rules[i] = this.rules[i].clone();
         this.rules[i].zoom = selector.zoom;
-        this.ruleIndex.push(this.rules[i].updateID());
+        this.ruleIndex[this.rules[i].updateID()] = true;
     }
     this.filters = selector.filters;
     this.zoom = selector.zoom;
@@ -35,7 +35,7 @@ tree.Definition.prototype.clone = function(filters) {
     if (filters) assert.ok(filters instanceof tree.Filterset);
     var clone = Object.create(tree.Definition.prototype);
     clone.rules = this.rules.slice();
-    clone.ruleIndex = this.ruleIndex.slice();
+    clone.ruleIndex = Object.create(this.ruleIndex);
     clone.filters = filters ? filters : this.filters.clone();
     clone.attachment = this.attachment;
     return clone;
@@ -46,9 +46,9 @@ tree.Definition.prototype.addRules = function(rules) {
 
     // Add only unique rules.
     for (var i = 0; i < rules.length; i++) {
-        if (this.ruleIndex.indexOf(rules[i].id) < 0) {
+        if (!this.ruleIndex[rules[i].id]) {
             this.rules.push(rules[i]);
-            this.ruleIndex.push(rules[i].id);
+            this.ruleIndex[rules[i].id] = true;
             added++;
         }
     }
@@ -60,7 +60,7 @@ tree.Definition.prototype.addRules = function(rules) {
 // and array of classes, by determining whether
 // all elements it contains match.
 tree.Definition.prototype.appliesTo = function(id, classes) {
-    for (var i = 0; i < this.elements.length; i++) {
+    for (var i = 0, l = this.elements.length; i < l; i++) {
         if (!this.elements[i].matches(id, classes)) {
             return false;
         }
diff --git a/lib/carto/tree/dimension.js b/lib/carto/tree/dimension.js
index aa631da..8db423e 100644
--- a/lib/carto/tree/dimension.js
+++ b/lib/carto/tree/dimension.js
@@ -12,7 +12,7 @@ tree.Dimension = function Dimension(value, unit, index) {
 tree.Dimension.prototype = {
     is: 'float',
     'eval': function (env) {
-        if (this.unit && ['px', '%'].indexOf(this.unit) === -1) {
+        if (this.unit && (this.unit !== 'px' && this.unit !== '%')) {
              env.error({
                 message: "Invalid unit: '" + this.unit + "'",
                 index: this.index
diff --git a/lib/carto/tree/element.js b/lib/carto/tree/element.js
index 1b06c5a..412e794 100644
--- a/lib/carto/tree/element.js
+++ b/lib/carto/tree/element.js
@@ -25,7 +25,7 @@ tree.Element.prototype.toString = function() {
 // Takes a plain string for id and plain strings in the array of
 // classes.
 tree.Element.prototype.matches = function(id, classes) {
-    return (classes.indexOf(this.value.replace(/^\./, '')) !== -1) ||
+    return (classes[this.value.replace(/^\./, '')]) ||
         (this.value.replace(/^#/, '') === id) ||
         (this.value === '*');
 };
diff --git a/lib/carto/tree/filterset.js b/lib/carto/tree/filterset.js
index 6e02605..889cbfd 100644
--- a/lib/carto/tree/filterset.js
+++ b/lib/carto/tree/filterset.js
@@ -65,9 +65,7 @@ tree.Filterset.prototype.cloneWith = function(other) {
 
     // We can add the rules that are already present without going through the
     // add function as a Filterset is always in it's simplest canonical form.
-    for (id in this.filters) {
-        clone.filters[id] = this.filters[id];
-    }
+    clone.filters = Object.create(this.filters);
 
     // Only add new filters that actually change the filter.
     while (id = additions.shift()) {
diff --git a/lib/carto/tree/layer.js b/lib/carto/tree/layer.js
index f36cfcf..dc2c9d9 100644
--- a/lib/carto/tree/layer.js
+++ b/lib/carto/tree/layer.js
@@ -1,32 +1,26 @@
 (function(tree) {
 
-tree.Layer = function Layer(obj) {
-    this.name = obj.name;
-    this.status = obj.status;
-    this.styles = obj.styles;
-    this.properties = obj.properties  || {};
-    this.srs = obj.srs;
-    this.datasource = obj.Datasource;
+tree.Layer = function Layer(obj, styles) {
 };
 
-tree.Layer.prototype.toXML = function() {
+tree.Layer.toXML = function(obj, styles) {
     var dsoptions = [];
-    for (var i in this.datasource) {
+    for (var i in obj.Datasource) {
         dsoptions.push('<Parameter name="' + i + '"><![CDATA[' +
-            this.datasource[i] + ']]></Parameter>');
+            obj.Datasource[i] + ']]></Parameter>');
     }
 
     var prop_string = '';
-    for (var prop in this.properties) {
-        prop_string += '  ' + prop + '="' + this.properties[prop] + '"\n';
+    for (var prop in obj.properties) {
+        prop_string += '  ' + prop + '="' + obj.properties[prop] + '"\n';
     }
 
     return '<Layer' +
-        ' name="' + this.name + '"\n' +
+        ' name="' + obj.name + '"\n' +
         prop_string +
-        ((typeof this.status === 'undefined') ? '' : '  status="' + this.status + '"\n') +
-        '  srs="' + this.srs + '">\n    ' +
-        this.styles.reverse().map(function(s) {
+        ((typeof obj.status === 'undefined') ? '' : '  status="' + obj.status + '"\n') +
+        '  srs="' + obj.srs + '">\n    ' +
+        styles.reverse().map(function(s) {
             return '<StyleName>' + s + '</StyleName>';
         }).join('\n    ') +
         '\n    <Datasource>\n       ' +
diff --git a/lib/carto/tree/reference.js b/lib/carto/tree/reference.js
index 5e7a25f..27716d4 100644
--- a/lib/carto/tree/reference.js
+++ b/lib/carto/tree/reference.js
@@ -4,7 +4,7 @@
 // combinations.
 (function(tree) {
 
-var _ = require('lodash');
+var _ = require('underscore');
 var mapnik_reference = require('mapnik-reference');
 
 tree.Reference = {
diff --git a/lib/carto/tree/style.js b/lib/carto/tree/style.js
index d05551d..9bf0d46 100644
--- a/lib/carto/tree/style.js
+++ b/lib/carto/tree/style.js
@@ -1,16 +1,12 @@
 (function(tree) {
-var _ = require('lodash');
+var _ = require('underscore');
 
 tree.Style = function Style(name, attachment, definitions) {
-    this.attachment = attachment;
-    this.definitions = definitions;
-    this.name = name + (attachment !== '__default__' ? '-' + attachment : '');
 };
 
-tree.Style.prototype.toXML = function(env) {
+tree.Style.toXML = function(name, attachment, definitions, env) {
     var existing = {};
 
-    var definitions = this.definitions;
     function byName(name) {
         return _.flatten(definitions.map(function(definition) {
             return definition.rules.filter(function(rule) {
@@ -23,7 +19,7 @@ tree.Style.prototype.toXML = function(env) {
     var comp_op = byName('comp-op');
     var opacity = byName('opacity');
 
-    var rules = this.definitions.map(function(definition) {
+    var rules = definitions.map(function(definition) {
         return definition.toXML(env, existing);
     });
 
@@ -43,7 +39,7 @@ tree.Style.prototype.toXML = function(env) {
         attrs_xml += ' opacity="' + opacity[0].value.eval(env).toString() + '" ';
     }
 
-    return '<Style name="' + this.name + '" filter-mode="first" ' + attrs_xml + '>\n' + rules.join('') + '</Style>';
+    return '<Style name="' + name + '" filter-mode="first" ' + attrs_xml + '>\n' + rules.join('') + '</Style>';
 };
 
 })(require('../tree'));
diff --git a/package.json b/package.json
index 28c2456..42a433e 100644
--- a/package.json
+++ b/package.json
@@ -37,8 +37,7 @@
   "dependencies": {
     "underscore": "~1.3.3",
     "mapnik-reference": "~5.0.0",
-    "xml2js": "~0.1.13",
-    "lodash": "~1.0.0-rc.3"
+    "xml2js": "~0.1.13"
   },
   "devDependencies": {
     "mocha": "1.3.x",