diff --git a/lib/less/tree/anonymous.js b/lib/less/tree/anonymous.js
index 460c9ec7..44614906 100644
--- a/lib/less/tree/anonymous.js
+++ b/lib/less/tree/anonymous.js
@@ -7,7 +7,21 @@ tree.Anonymous.prototype = {
     toCSS: function () {
         return this.value;
     },
-    eval: function () { return this }
+    eval: function () { return this },
+    compare: function (x) {
+        if (!x.toCSS) {
+            return -1;
+        }
+        
+        var left = this.toCSS(),
+            right = x.toCSS();
+        
+        if (left === right) {
+            return 0;
+        }
+        
+        return left < right ? -1 : 1;
+    }
 };
 
 })(require('../tree'));
diff --git a/lib/less/tree/color.js b/lib/less/tree/color.js
index 37ce1781..6adf3179 100644
--- a/lib/less/tree/color.js
+++ b/lib/less/tree/color.js
@@ -94,6 +94,16 @@ tree.Color.prototype = {
             i = (i > 255 ? 255 : (i < 0 ? 0 : i)).toString(16);
             return i.length === 1 ? '0' + i : i;
         }).join('');
+    },
+    compare: function (x) {
+        if (!x.rgb) {
+            return -1;
+        }
+        
+        return (x.rgb[0] === this.rgb[0] &&
+            x.rgb[1] === this.rgb[1] &&
+            x.rgb[2] === this.rgb[2] &&
+            x.alpha === this.alpha) ? 0 : -1;
     }
 };
 
diff --git a/lib/less/tree/quoted.js b/lib/less/tree/quoted.js
index 794bf4ce..f93dc8e1 100644
--- a/lib/less/tree/quoted.js
+++ b/lib/less/tree/quoted.js
@@ -23,6 +23,20 @@ tree.Quoted.prototype = {
             return ('value' in v) ? v.value : v.toCSS();
         });
         return new(tree.Quoted)(this.quote + value + this.quote, value, this.escaped, this.index);
+    },
+    compare: function (x) {
+        if (!x.toCSS) {
+            return -1;
+        }
+        
+        var left = this.toCSS(),
+            right = x.toCSS();
+        
+        if (left === right) {
+            return 0;
+        }
+        
+        return left < right ? -1 : 1;
     }
 };
 
diff --git a/lib/less/tree/ruleset.js b/lib/less/tree/ruleset.js
index 80203f90..f5f397ef 100644
--- a/lib/less/tree/ruleset.js
+++ b/lib/less/tree/ruleset.js
@@ -10,7 +10,8 @@ tree.Ruleset.prototype = {
     eval: function (env) {
         var selectors = this.selectors && this.selectors.map(function (s) { return s.eval(env) });
         var ruleset = new(tree.Ruleset)(selectors, this.rules.slice(0), this.strictImports);
-
+        var rules = [];
+        
         ruleset.root = this.root;
         ruleset.allowImports = this.allowImports;
 
@@ -21,10 +22,13 @@ tree.Ruleset.prototype = {
         if (ruleset.root || ruleset.allowImports || !ruleset.strictImports) {
             for (var i = 0; i < ruleset.rules.length; i++) {
                 if (ruleset.rules[i] instanceof tree.Import) {
-                    Array.prototype.splice
-                         .apply(ruleset.rules, [i, 1].concat(ruleset.rules[i].eval(env)));
+                    rules = rules.concat(ruleset.rules[i].eval(env));
+                } else {
+                    rules.push(ruleset.rules[i]);
                 }
             }
+            ruleset.rules = rules;
+            rules = [];
         }
 
         // Store the frames around mixin definitions,
@@ -38,10 +42,12 @@ tree.Ruleset.prototype = {
         // Evaluate mixin calls.
         for (var i = 0; i < ruleset.rules.length; i++) {
             if (ruleset.rules[i] instanceof tree.mixin.Call) {
-                Array.prototype.splice
-                     .apply(ruleset.rules, [i, 1].concat(ruleset.rules[i].eval(env)));
+                rules = rules.concat(ruleset.rules[i].eval(env));
+            } else {
+                rules.push(ruleset.rules[i]);
             }
         }
+        ruleset.rules = rules;
 
         // Evaluate everything else
         for (var i = 0, rule; i < ruleset.rules.length; i++) {
diff --git a/test/css/mixins-guards.css b/test/css/mixins-guards.css
index 0c563e52..cd94c010 100644
--- a/test/css/mixins-guards.css
+++ b/test/css/mixins-guards.css
@@ -56,3 +56,13 @@
   content: not false;
   content: not false and false, not false;
 }
+.colorguardtest {
+  content: is #ff0000;
+  content: is not #0000ff its #ff0000;
+  content: is not #0000ff its #800080;
+}
+.stringguardtest {
+  content: is theme1;
+  content: is not theme2;
+  content: is theme1 no quotes;
+}
diff --git a/test/less-test.js b/test/less-test.js
index 806fe1d0..57f7aa3d 100644
--- a/test/less-test.js
+++ b/test/less-test.js
@@ -29,7 +29,7 @@ fs.readdirSync('test/less').forEach(function (file) {
             else if (err) {
                 sys.print(stylize("ERROR: " + (err && err.message), 'red'));
             } else {
-                sys.print(stylize("FAIL", 'yellow'));
+                sys.print(stylize("FAIL", 'yellow') + '\n');
                 
                 require('diff').diffLines(css, less).forEach(function(item) {
                   if(item.added || item.removed) {
diff --git a/test/less/mixins-guards.less b/test/less/mixins-guards.less
index 1f46e976..3e27c268 100644
--- a/test/less/mixins-guards.less
+++ b/test/less/mixins-guards.less
@@ -92,3 +92,22 @@
 .bool () when not (false) and (false), not (false)           { content: not false and false, not false }
 
 .bool1 { .bool }
+
+.colorguard(@col) when (@col = red)							{ content: is @col; }
+.colorguard(@col) when not (blue = @col)					{ content: is not blue its @col; }
+.colorguard(@col)											{}
+.colorguardtest {
+    .colorguard(red);
+	.colorguard(blue);
+	.colorguard(purple);
+}
+
+.stringguard(@str) when (@str = "theme1")					{ content: is theme1; }
+.stringguard(@str) when not ("theme2" = @str)				{ content: is not theme2; }
+.stringguard(@str) when (~"theme1" = @str)					{ content: is theme1 no quotes; }
+.stringguard(@str)											{}
+.stringguardtest {
+    .stringguard("theme1");
+	.stringguard("theme2");
+	.stringguard(theme1);
+}
\ No newline at end of file