diff --git a/lib/less/tree/ruleset.js b/lib/less/tree/ruleset.js
index e6e582c4..9f7eb2a3 100644
--- a/lib/less/tree/ruleset.js
+++ b/lib/less/tree/ruleset.js
@@ -47,7 +47,15 @@ tree.Ruleset.prototype = {
         // Evaluate mixin calls.
         for (var i = 0; i < ruleset.rules.length; i++) {
             if (ruleset.rules[i] instanceof tree.mixin.Call) {
-                rules = ruleset.rules[i].eval(env);
+                rules = ruleset.rules[i].eval(env).filter(function(r) {
+                    if ((r instanceof tree.Rule) && r.variable) {
+                        // do not pollute the scope if the variable is
+                        // already there. consider returning false here
+                        // but we need a way to "return" variable from mixins
+                        return !(ruleset.variable(r.name));
+                    }
+                    return true;
+                });
                 ruleset.rules.splice.apply(ruleset.rules, [i, 1].concat(rules));
                 i += rules.length-1;
                 ruleset.resetCache();
diff --git a/test/css/variables.css b/test/css/variables.css
index 27006ecb..31e25894 100644
--- a/test/css/variables.css
+++ b/test/css/variables.css
@@ -26,7 +26,7 @@
   filter: alpha(opacity=42);
 }
 .testPollution {
-  a: 'pollution';
+  a: 'no-pollution';
 }
 .units {
   width: 1px;
diff --git a/test/less/variables.less b/test/less/variables.less
index b53b8603..0974864a 100644
--- a/test/less/variables.less
+++ b/test/less/variables.less
@@ -56,11 +56,11 @@
     filter: alpha(opacity=@var);
 }
 
-// test current behaviour
 .polluteMixin() {
     @a: 'pollution';
 }
 .testPollution {
+    @a: 'no-pollution';
     a: @a;
 	.polluteMixin();
 	a: @a;