diff --git a/lib/mess/index.js b/lib/mess/index.js
index 8da86f2..7be7d35 100644
--- a/lib/mess/index.js
+++ b/lib/mess/index.js
@@ -10,7 +10,7 @@ var mess = {
     Renderer: require('mess/renderer').Renderer,
     importer: require('mess/parser').importer,
     tree: require('mess/tree'),
-    render: function (input, options, callback) {
+    render: function(input, options, callback) {
         options = options || {};
 
         if (typeof(options) === 'function') {
@@ -21,23 +21,23 @@ var mess = {
             ee;
 
         if (callback) {
-            parser.parse(input, function (e, root) {
+            parser.parse(input, function(e, root) {
                 callback(e, root.toCSS());
             });
         } else {
             ee = new(require('events').EventEmitter);
 
-            process.nextTick(function () {
-                parser.parse(input, function (e, root) {
+            process.nextTick(function() {
+                parser.parse(input, function(e, root) {
                     if (e) { ee.emit('error', e) }
-                    else   { ee.emit('success', root.toCSS()) }
+                    else { ee.emit('success', root.toCSS()) }
                 });
             });
             return ee;
         }
     },
-    writeError: function (ctx, options) {
-        var message = "";
+    writeError: function(ctx, options) {
+        var message = '';
         var extract = ctx.extract;
         var error = [];
 
@@ -70,24 +70,24 @@ var mess = {
         sys.error(message, error);
 
         if (ctx.callLine) {
-            sys.error(stylize('from ', 'red')       + (ctx.filename || ''));
+            sys.error(stylize('from ', 'red') + (ctx.filename || ''));
             sys.error(stylize(ctx.callLine, 'grey') + ' ' + ctx.callExtract);
         }
         if (ctx.stack) { sys.error(stylize(ctx.stack, 'red')) }
     }
 };
 
-['color',    'directive', 'operation',  'dimension',
- 'keyword',  'variable',  'ruleset',    'element',
- 'selector', 'quoted',    'expression', 'rule',
- 'call',     'url',       'alpha',      'import',
- 'mixin',    'comment',   'anonymous',  'value', 'javascript',
- 'comparison', 'reference', 'filter', 'zoomfilter'
-].forEach(function (n) {
+['color', 'directive', 'operation', 'dimension',
+ 'keyword', 'variable', 'ruleset', 'element',
+ 'selector', 'quoted', 'expression', 'rule',
+ 'call', 'url', 'alpha', 'import',
+ 'mixin', 'comment', 'anonymous', 'value', 'javascript',
+ 'comparison', 'reference', 'filter', 'definition', 'zoomfilter'
+].forEach(function(n) {
     require(path.join('mess', 'tree', n));
 });
 
-mess.Parser.importer = function (file, paths, callback) {
+mess.Parser.importer = function(file, paths, callback) {
     var pathname;
 
     paths.unshift('.');
@@ -109,7 +109,7 @@ mess.Parser.importer = function (file, paths, callback) {
           new(mess.Parser)({
               paths: [path.dirname(pathname)],
               filename: pathname
-          }).parse(data, function (e, root) {
+          }).parse(data, function(e, root) {
               if (e) mess.writeError(e);
               callback(root);
           });
@@ -118,7 +118,7 @@ mess.Parser.importer = function (file, paths, callback) {
         sys.error("file '" + file + "' wasn't found.\n");
         process.exit(1);
     }
-}
+};
 
 require('mess/functions');
 
@@ -127,13 +127,13 @@ for (var k in mess) { exports[k] = mess[k] }
 // Stylize a string
 function stylize(str, style) {
     var styles = {
-        'bold'      : [1,  22],
-        'inverse'   : [7,  27],
-        'underline' : [4,  24],
-        'yellow'    : [33, 39],
-        'green'     : [32, 39],
-        'red'       : [31, 39],
-        'grey'      : [90, 39]
+        'bold' : [1, 22],
+        'inverse' : [7, 27],
+        'underline' : [4, 24],
+        'yellow' : [33, 39],
+        'green' : [32, 39],
+        'red' : [31, 39],
+        'grey' : [90, 39]
     };
     return '\033[' + styles[style][0] + 'm' + str +
            '\033[' + styles[style][1] + 'm';
diff --git a/lib/mess/parser.js b/lib/mess/parser.js
index a5ed03d..7994c41 100644
--- a/lib/mess/parser.js
+++ b/lib/mess/parser.js
@@ -314,10 +314,9 @@ mess.Parser = function Parser(env) {
                         options.compress : (env.compress || false);
 
                     try {
-                        var rulesets = this.flatten();
-                        rulesets = splitSelectors(rulesets);
-                        rulesets.sort(specificitySort);
-                        return rulesets;
+                        var definitions = this.flatten([]);
+                        definitions.sort(specificitySort);
+                        return definitions;
                     }
                     catch (e) {
                         lines = input.split('\n');
@@ -351,15 +350,6 @@ mess.Parser = function Parser(env) {
                 };
             })();
 
-            var splitSelectors = function(rulesets) {
-                return rulesets.reduce(function(result, ruleset) {
-                    ruleset.selectors.forEach(function(selector) {
-                       result.push({ selector: selector, rules: ruleset.rules });
-                    });
-                    return result;
-                }, []);
-            };
-
             /**
              * Sort rules by specificity: this function expects selectors to be
              * split already.
diff --git a/lib/mess/tree/definition.js b/lib/mess/tree/definition.js
new file mode 100644
index 0000000..0e91eab
--- /dev/null
+++ b/lib/mess/tree/definition.js
@@ -0,0 +1,8 @@
+(function(tree) {
+
+tree.Definition = function(selector, rules) {
+    this.selector = selector;
+    this.rules = rules;
+};
+
+})(require('mess/tree'));
diff --git a/lib/mess/tree/ruleset.js b/lib/mess/tree/ruleset.js
index 45aaa42..6125be0 100644
--- a/lib/mess/tree/ruleset.js
+++ b/lib/mess/tree/ruleset.js
@@ -131,7 +131,7 @@ tree.Ruleset.prototype = {
     },
 
 
-    flatten: function(parentSelectors) {
+    flatten: function(result, parentSelectors) {
         var selectors = [];
         for (var i = 0; i < this.selectors.length; i++) {
             var selector = this.selectors[i];
@@ -156,12 +156,11 @@ tree.Ruleset.prototype = {
         }
 
         var rules = [];
-        var rulesets = [];
         for (var i = 0; i < this.rules.length; i++) {
             var rule = this.rules[i];
 
             if (rule instanceof tree.Ruleset) {
-                Array.prototype.push.apply(rulesets, rule.flatten(selectors));
+                rule.flatten(result, selectors);
             }
             else {
                 rule.value = rule.value.value[0];
@@ -169,11 +168,11 @@ tree.Ruleset.prototype = {
             }
         }
 
-        var ruleset = new tree.Ruleset(selectors, rules);
-        ruleset.flattened = true;
-        rulesets.push(ruleset);
+        for (var i = 0; i < selectors.length; i++) {
+            result.push(new tree.Definition(selectors[i], rules));
+        }
 
-        return rulesets;
+        return result;
     },
 
     toMSS: function(env) {