diff --git a/lib/propmangle.js b/lib/propmangle.js
index 4187db121c5..52705393fc1 100644
--- a/lib/propmangle.js
+++ b/lib/propmangle.js
@@ -83,7 +83,8 @@ function mangle_properties(ast, options) {
         cache : null,
         only_cache : false,
         regex : null,
-        ignore_quoted : false
+        ignore_quoted : false,
+        treat_as_global : [],
     });
 
     var reserved = options.reserved;
@@ -104,7 +105,17 @@ function mangle_properties(ast, options) {
     var names_to_mangle = [];
     var unmangleable = [];
     var ignored = {};
-
+    
+    if (!cache.global_defs) cache.global_defs = {};
+    
+    var treat_as_global = options.treat_as_global;
+    var mangle_globals = !!treat_as_global.length;
+    
+    function is_global_alias(name)
+    {
+        return treat_as_global.indexOf(name) >= 0;
+    }
+    
     // step 1: find candidates to mangle
     ast.walk(new TreeWalker(function(node){
         if (node instanceof AST_ObjectKeyVal) {
@@ -116,6 +127,16 @@ function mangle_properties(ast, options) {
         }
         else if (node instanceof AST_Dot) {
             add(node.property);
+            
+            // if the left side of the dot is a global alias (e.g. window.foo), and the left side
+            // does not refer to a local variable, add it to a list of global definitions.
+            if (mangle_globals &&
+                node.expression instanceof AST_SymbolRef &&
+                node.expression.global() &&
+                is_global_alias(node.expression.name) &&
+                !is_global_alias(node.property)) {
+                cache.global_defs[node.property] = true;
+            }
         }
         else if (node instanceof AST_Sub) {
             addStrings(node.property, ignore_quoted);
@@ -123,6 +144,15 @@ function mangle_properties(ast, options) {
         else if (node instanceof AST_ConciseMethod) {
             add(node.name.name);
         }
+        else if (node instanceof AST_SymbolRef) {
+            // if this term stands alone (e.g. just 'foo' where 'foo' cannot be shown to
+            // be a local variable in scope), also treat it as a global definition.
+            if (mangle_globals &&
+                node.global() &&
+                !is_global_alias(node.name)) {
+                cache.global_defs[node.name] = true;
+            }
+        }
     }));
 
     // step 2: transform the tree, renaming properties
@@ -147,6 +177,17 @@ function mangle_properties(ast, options) {
                 node.name.name = mangle(node.name.name);
             }
         }
+        else if (node instanceof AST_SymbolRef) {
+            // if this is a standalone global reference which does not refer to a local variable in scope,
+            // and it's on our list of global definitions, then mangle it.
+            if (mangle_globals &&
+                node.global() &&
+                node.name in cache.global_defs) {
+                var mangled_name = mangle(node.name);
+                node.name = mangled_name;
+                node.definition().mangled_name = mangled_name;
+            }
+        }
         // else if (node instanceof AST_String) {
         //     if (should_mangle(node.value)) {
         //         AST_Node.warn(
@@ -178,7 +219,8 @@ function mangle_properties(ast, options) {
         if (regex && !regex.test(name)) return false;
         if (reserved.indexOf(name) >= 0) return false;
         return cache.props.has(name)
-            || names_to_mangle.indexOf(name) >= 0;
+            || names_to_mangle.indexOf(name) >= 0
+            || (mangle_globals && name in cache.global_defs);
     }
 
     function add(name, ignore) {
@@ -205,6 +247,12 @@ function mangle_properties(ast, options) {
             do {
                 mangled = base54(++cache.cname);
             } while (!can_mangle(mangled));
+            
+            // HACK: to avoid mangled global references colliding with local variable names, use
+            // a prefix on all mangled global names to effectively move them to a different namespace.
+            if (mangle_globals && name in cache.global_defs)
+                mangled = "g_" + mangled;
+            
             cache.props.set(name, mangled);
         }
         return mangled;
diff --git a/test/compress/properties.js b/test/compress/properties.js
index 7ef6a014d86..94b6434fc64 100644
--- a/test/compress/properties.js
+++ b/test/compress/properties.js
@@ -143,6 +143,52 @@ mangle_unquoted_properties: {
     }
 }
 
+mangle_global_properties: {
+    mangle_props = {
+        treat_as_global: ["window"],
+        reserved: ["console", "log"]
+    }
+    input: {
+        window.foo = {};
+        foo.bar = 1;
+        external.baz = 2;
+        console.log(external);
+    }
+    expect: {
+        window.g_a = {};
+        g_a.b = 1;
+        g_d.c = 2;
+        console.log(g_d);
+    }
+}
+
+mangle_global_properties_not_local: {
+    options = {
+    }
+    mangle_props = {
+        treat_as_global: ["self"],
+        reserved: ["console", "log"]
+    }
+    input: {
+        self.foo = {};
+        function test()
+        {
+            var self = this;
+            console.log(self.bar);
+        };
+        console.log(typeof bar);
+    }
+    expect: {
+        self.g_a = {};
+        function test()
+        {
+            var self = this;
+            console.log(self.b);
+        };
+        console.log(typeof g_b);
+    }
+}
+
 first_256_chars_as_properties: {
     beautify = {
         ascii_only: true,