diff --git a/Gruntfile.js b/Gruntfile.js
index d8c264ba..a59914c1 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -41,6 +41,8 @@ module.exports = function(grunt) {
         build_dir: "build",
         //Parser lib copy for versions that can't use requirejs
         parserlib: "node_modules/parserlib/lib/node-parserlib.js",
+        //clone copy for versions that can't use requirejs
+        clone: "node_modules/clone/clone.js",
         //Core CSSLint files used by most versions
         csslint_files: [
             "src/core/CSSLint.js",
@@ -51,6 +53,7 @@ module.exports = function(grunt) {
         //Core fileset used by most versions
         core_files: [
             "<%= parserlib %>",
+            "<%= clone %>",
             "<%= csslint_files %>"
         ],
         // Task configuration.
@@ -86,6 +89,7 @@ module.exports = function(grunt) {
             node: {
                 options: {
                     banner: "<%= banner.full %>\n" +
+                            "var clone = require('clone');\n" +
                             "var parserlib = require('parserlib');\n",
                     footer: "\nexports.CSSLint = CSSLint;"
                 },
diff --git a/package.json b/package.json
index 013a6fe8..eee7f7c6 100644
--- a/package.json
+++ b/package.json
@@ -26,6 +26,7 @@
     "test": "grunt test"
   },
   "dependencies": {
+    "clone": "~0.1.11",
     "parserlib": "~0.2.4"
   },
   "devDependencies": {
diff --git a/src/core/CSSLint.js b/src/core/CSSLint.js
index 61e41706..9c4f84ba 100644
--- a/src/core/CSSLint.js
+++ b/src/core/CSSLint.js
@@ -5,7 +5,7 @@
  * @extends parserlib.util.EventTarget
  */
 
-/* global parserlib, Reporter */
+/* global parserlib, clone, Reporter */
 /* exported CSSLint */
 
 var CSSLint = (function(){
@@ -189,6 +189,8 @@ var CSSLint = (function(){
         }
 
         if (embeddedRuleset.test(text)){
+            //defensively copy so that caller's version does not get modified
+            ruleset = clone(ruleset);
             ruleset = applyEmbeddedRuleset(text, ruleset);
         }
 
diff --git a/tests/core/CSSLint.js b/tests/core/CSSLint.js
index 09627707..967feb5b 100644
--- a/tests/core/CSSLint.js
+++ b/tests/core/CSSLint.js
@@ -25,6 +25,18 @@
             Assert.areEqual(2, result.ruleset["adjoining-classes"]);
             Assert.areEqual(1, result.ruleset["text-indent"]);
             Assert.areEqual(0, result.ruleset["box-sizing"]);
+        },
+
+        "Embedded rulesets should not have the side-effect of modifying the ruleset object passed in by the caller of verify()": function(){
+            var ruleset = {
+                "text-indent": 1,
+                "box-sizing": 1
+            };
+            CSSLint.verify("/*csslint bogus, adjoining-classes:true, box-sizing:false */\n.foo.bar{}", ruleset);
+
+            Assert.areEqual(undefined, ruleset["adjoining-classes"]);
+            Assert.areEqual(1, ruleset["text-indent"]);
+            Assert.areEqual(1, ruleset["box-sizing"]);
         }
 
     }));