diff --git a/README.md b/README.md
index a8b55843db..9825afc74f 100644
--- a/README.md
+++ b/README.md
@@ -150,6 +150,7 @@ The available options are:
                                 notation. You can override these by setting
                                 them explicitly on the command line.
   --mangle-regex                Only mangle property names matching the regex
+  --mangle-props-prefix         Prefix added to the property name after mangling
   --name-cache                  File to hold mangled names mappings
   --pure-funcs                  List of functions that can be safely removed if
                                 their return value is not used           [array]
diff --git a/bin/uglifyjs b/bin/uglifyjs
index 8cb2f0df7c..da0379da84 100755
--- a/bin/uglifyjs
+++ b/bin/uglifyjs
@@ -74,6 +74,7 @@ You need to pass an argument to this option to specify the name that your module
     .describe("reserve-domprops", "Make (most?) DOM properties reserved for --mangle-props")
     .describe("mangle-props", "Mangle property names (0 - disabled, 1 - mangle all properties, 2 - mangle unquoted properies)")
     .describe("mangle-regex", "Only mangle property names matching the regex")
+    .describe("mangle-props-prefix", "Prefix added to the property name after mangling")
     .describe("name-cache", "File to hold mangled names mappings")
     .describe("pure-funcs", "List of functions that can be safely removed if their return value is not used")
     .describe("dump-spidermonkey-ast", "Dump SpiderMonkey AST to stdout.")
@@ -110,6 +111,7 @@ You need to pass an argument to this option to specify the name that your module
     .string("p")
     .string("prefix")
     .string("name-cache")
+    .string("mangle-props-prefix")
 
     .array("reserved-file")
     .array("pure-funcs")
@@ -421,6 +423,7 @@ async.eachLimit(files, 1, function (file, cb) {
             only_cache    : !ARGS.mangle_props,
             regex         : regex,
             ignore_quoted : ARGS.mangle_props == 2,
+            prefix        : ARGS.mangle_props_prefix || "",
             debug         : typeof ARGS.mangle_props_debug === "undefined" ? false : ARGS.mangle_props_debug
         });
         writeNameCache("props", cache);
diff --git a/lib/propmangle.js b/lib/propmangle.js
index f2777475d2..e40f5c6ad5 100644
--- a/lib/propmangle.js
+++ b/lib/propmangle.js
@@ -67,7 +67,8 @@ function mangle_properties(ast, options) {
         only_cache : false,
         regex : null,
         ignore_quoted : false,
-        debug : false
+        debug : false,
+        prefix: ""
     });
 
     var reserved = options.reserved;
@@ -202,7 +203,7 @@ function mangle_properties(ast, options) {
                 // (filled with quoted properties when ignore_quoted set). Make sure we add this
                 // check so we don't collide with a quoted name.
                 do {
-                    mangled = base54(++cache.cname);
+                    mangled = options.prefix + base54(++cache.cname);
                 } while (!can_mangle(mangled) || (ignore_quoted && mangled in ignored));
             }
 
diff --git a/test/compress/mangle-prefix.js b/test/compress/mangle-prefix.js
new file mode 100644
index 0000000000..f8e5dd32e6
--- /dev/null
+++ b/test/compress/mangle-prefix.js
@@ -0,0 +1,57 @@
+prefix_no_debug: {
+    mangle_props = {
+        ignore_quoted: true,
+        prefix: "__"
+    }
+    input: {
+        var x = {};
+        x.foo = 1;
+        x["a"] = 2 * x.foo;
+        console.log(x.foo, x["a"]);
+    }
+    expect: {
+        var x = {};
+        x.__a = 1;
+        x["a"] = 2 * x.__a;
+        console.log(x.__a, x["a"]);
+    }
+}
+
+prefix_debug: {
+    mangle_props = {
+        ignore_quoted: true,
+        debug: "",
+        prefix: "__"
+    }
+    input: {
+        var x = {};
+        x.foo = 1;
+        x["_$foo$_"] = 2 * x.foo;
+        console.log(x.foo, x["_$foo$_"]);
+    }
+    expect: {
+        var x = {};
+        x.__a = 1;
+        x["_$foo$_"] = 2 * x.__a;
+        console.log(x.__a, x["_$foo$_"]);
+    }
+}
+
+prefix_with_quoted: {
+    mangle_props = {
+        ignore_quoted: false,
+        prefix: "__"
+    }
+    input: {
+        var x = {};
+        x.foo = 1;
+        x["a"] = 2 * x.foo;
+        console.log(x.foo, x["a"]);
+    }
+    expect: {
+        var x = {};
+        x.__a = 1;
+        x["__b"] = 2 * x.__a;
+        console.log(x.__a, x["__b"]);
+    }
+}
diff --git a/test/input/mangle-prefix/sample.js b/test/input/mangle-prefix/sample.js
new file mode 100644
index 0000000000..899782b736
--- /dev/null
+++ b/test/input/mangle-prefix/sample.js
@@ -0,0 +1,20 @@
+var Test = function() {
+  this.someVar = 123;
+};
+
+Test.prototype.someMethod = function() {
+  console.log(this.someVar);
+}
+
+Test.prototype.someOther = function() {
+  console.log("other");
+  this.someMethod();
+  this.__special();
+}
+
+Test.prototype.__special = function() {
+  console.log("special");
+}
+
+var oTest = new Test();
+oTest.someOther();
diff --git a/test/mocha/cli.js b/test/mocha/cli.js
index a8de05c525..b8bfb6f34d 100644
--- a/test/mocha/cli.js
+++ b/test/mocha/cli.js
@@ -100,4 +100,24 @@ describe("bin/uglifyjs", function () {
            done();
        });
     });
+    it("Should work with --mangle-props-prefix", function (done) {
+       var command = uglifyjscmd + ' test/input/mangle-prefix/sample.js --mangle-props --mangle-props-prefix="__"';
+
+       exec(command, function (err, stdout) {
+           if (err) throw err;
+
+           assert.strictEqual(stdout, "var Test=function(){this.__a=123};Test.prototype.__b=function(){console.log(this.__a)};Test.prototype.__c=function(){console.log(\"other\");this.__b();this.__d()};Test.prototype.__d=function(){console.log(\"special\")};var oTest=new Test;oTest.__c();\n");
+           done();
+       });
+    });
+    it("Should work with --mangle-props-prefix and --mangle-props-regex", function (done) {
+       var command = uglifyjscmd + ' test/input/mangle-prefix/sample.js --mangle-props --mangle-regex="/^__/" --mangle-props-prefix="__"';
+
+       exec(command, function (err, stdout) {
+           if (err) throw err;
+
+           assert.strictEqual(stdout, "var Test=function(){this.someVar=123};Test.prototype.someMethod=function(){console.log(this.someVar)};Test.prototype.someOther=function(){console.log(\"other\");this.someMethod();this.__a()};Test.prototype.__a=function(){console.log(\"special\")};var oTest=new Test;oTest.someOther();\n");
+           done();
+       });
+    });
 });
diff --git a/test/mocha/minify.js b/test/mocha/minify.js
index 70cf73ae1b..f04c847af9 100644
--- a/test/mocha/minify.js
+++ b/test/mocha/minify.js
@@ -58,6 +58,44 @@ describe("minify", function() {
             assert.strictEqual(result.code,
                     'a["foo"]="bar",a.a="red",x={"bar":10};');
         });
+
+        it("Should add prefix for mangle properties (not quoted)", function() {
+            var js = 'a["foo"] = "bar"; a.color = "red"; x = {"bar": 10};';
+            var result = Uglify.minify(js, {
+                fromString: true,
+                compress: {
+                    properties: false
+                },
+                mangleProperties: {
+                    ignore_quoted: true,
+                    prefix: "__"
+                },
+                output: {
+                    keep_quoted_props: true,
+                    quote_style: 3
+                }
+            });
+            assert.strictEqual(result.code, 'a["foo"]="bar",a.__a="red",x={"bar":10};');
+        });
+
+        it("Should add prefix for mangle properties (with quoted)", function() {
+            var js = 'a["foo"] = "bar"; a.color = "red"; x = {"bar": 10};';
+            var result = Uglify.minify(js, {
+                fromString: true,
+                compress: {
+                    properties: false
+                },
+                mangleProperties: {
+                    ignore_quoted: false,
+                    prefix: "__"
+                },
+                output: {
+                    keep_quoted_props: true,
+                    quote_style: 3
+                }
+            });
+            assert.strictEqual(result.code, 'a["__a"]="bar",a.__b="red",x={"__c":10};');
+        });
     });
 
     describe("inSourceMap", function() {