diff --git a/lib/less/node/ruleset.js b/lib/less/node/ruleset.js
index f4515ec3..b5f84728 100644
--- a/lib/less/node/ruleset.js
+++ b/lib/less/node/ruleset.js
@@ -38,12 +38,15 @@ tree.Ruleset.prototype = {
     //
     // Entry point for code generation
     //
+    //     `context` holds an array of arrays.
+    //
     toCSS: function (context, env) {
         var css = [],      // The CSS output
             rules = [],    // node.Rule instances
             rulesets = [], // node.Ruleset instances
             paths = [],    // Current selectors
-            selector;      // The fully rendered selector
+            selector,      // The fully rendered selector
+            rule;
 
         if (! this.root) {
             if (context.length === 0) {
@@ -56,22 +59,29 @@ tree.Ruleset.prototype = {
                 }
             }
         }
+        // push the current ruleset to the frames stack
         env.frames.unshift(this);
 
+        // Evaluate mixins
         for (var i = 0; i < this.rules.length; i++) {
             if (this.rules[i] instanceof tree.mixin.Call) {
                 Array.prototype.splice
                      .apply(this.rules, [i, 1].concat(this.rules[i].eval(env)));
             }
         }
+
+        // Evaluate rules and rulesets
         for (var i = 0; i < this.rules.length; i++) {
-            if (this.rules[i] instanceof tree.Ruleset) {
-                rulesets.push(this.rules[i].toCSS(paths, env));
+            rule = this.rules[i];
+
+            if (rule instanceof tree.Ruleset ||
+               (rule instanceof tree.Directive && rule.rules)) {
+                rulesets.push(rule.toCSS(paths, env));
             } else {
-                if (this.rules[i].toCSS && !this.rules[i].variable) {
-                    rules.push(this.rules[i].toCSS(env));
-                } else if (this.rules[i].value && !this.rules[i].variable) {
-                    rules.push(this.rules[i].value.toString());    
+                if (rule.toCSS && !rule.variable) {
+                    rules.push(rule.toCSS(env));
+                } else if (rule.value && !rule.variable) {
+                    rules.push(rule.value.toString());
                 }
             }
         }