diff --git a/lib/less/tree/quoted.js b/lib/less/tree/quoted.js
index 131bfad9..b8f63b9c 100644
--- a/lib/less/tree/quoted.js
+++ b/lib/less/tree/quoted.js
@@ -33,14 +33,22 @@ tree.Quoted.prototype = {
         if (!x.toCSS) {
             return -1;
         }
-        
-        var left = this.toCSS(),
+
+        var left, right;
+
+        // when comparing quoted strings allow the quote to differ
+        if (x.type === "Quoted" && !this.escaped && !x.escaped) {
+            left = x.value;
+            right = this.value;
+        } else {
+            left = this.toCSS();
             right = x.toCSS();
-        
+        }
+
         if (left === right) {
             return 0;
         }
-        
+
         return left < right ? -1 : 1;
     }
 };
diff --git a/test/css/mixins-guards.css b/test/css/mixins-guards.css
index 25e6f287..27fa9762 100644
--- a/test/css/mixins-guards.css
+++ b/test/css/mixins-guards.css
@@ -67,9 +67,17 @@
   content: is not #0000ff its #800080;
 }
 .stringguardtest {
-  content: is theme1;
-  content: is not theme2;
-  content: is theme1 no quotes;
+  content: "theme1" is "theme1";
+  content: "theme1" is not "theme2";
+  content: "theme1" is 'theme1';
+  content: "theme1" is not 'theme2';
+  content: 'theme1' is "theme1";
+  content: 'theme1' is not "theme2";
+  content: 'theme1' is 'theme1';
+  content: 'theme1' is not 'theme2';
+  content: theme1 is not "theme2";
+  content: theme1 is not 'theme2';
+  content: theme1 is theme1;
 }
 #tryNumberPx {
   catch: all;
diff --git a/test/less/mixins-guards.less b/test/less/mixins-guards.less
index 6a02067b..62dc39df 100644
--- a/test/less/mixins-guards.less
+++ b/test/less/mixins-guards.less
@@ -116,13 +116,17 @@
 	.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) when (@str = "theme1")					{ content: @str is "theme1"; }
+.stringguard(@str) when not ("theme2" = @str)				{ content: @str is not "theme2"; }
+.stringguard(@str) when (@str = 'theme1')					{ content: @str is 'theme1'; }
+.stringguard(@str) when not ('theme2' = @str)				{ content: @str is not 'theme2'; }
+.stringguard(@str) when (~"theme1" = @str)					{ content: @str is theme1; }
 .stringguard(@str)											{}
 .stringguardtest {
     .stringguard("theme1");
 	.stringguard("theme2");
+    .stringguard('theme1');
+    .stringguard('theme2');
 	.stringguard(theme1);
 }