diff --git a/README.md b/README.md
index 40b2e1a0..8d07cfcd 100644
--- a/README.md
+++ b/README.md
@@ -76,7 +76,7 @@ The available options are:
                                 `debug`  Add debug prefix and suffix.
                                 `domprops`  Mangle property names that overlaps
                                             with DOM properties.
-                                `ignore_quoted`  Only mangle unquoted properies.
+                                `keep_quoted`  Only mangle unquoted properies.
                                 `regex`  Only mangle matched property names.
                                 `reserved`  List of names that should not be mangled.
     -b, --beautify [options]    Beautify output/specify output options:
@@ -256,14 +256,14 @@ of mangled property names.
 Using the name cache is not necessary if you compress all your files in a
 single call to UglifyJS.
 
-#### Mangling unquoted names (`--mangle-props ignore_quoted`)
+#### Mangling unquoted names (`--mangle-props keep_quoted`)
 
 Using quoted property name (`o["foo"]`) reserves the property name (`foo`)
 so that it is not mangled throughout the entire script even when used in an
 unquoted style (`o.foo`). Example:
 
 ```
-$ echo 'var o={"foo":1, bar:3}; o.foo += o.bar; console.log(o.foo);' | uglifyjs --mangle-props ignore_quoted -mc
+$ echo 'var o={"foo":1, bar:3}; o.foo += o.bar; console.log(o.foo);' | uglifyjs --mangle-props keep_quoted -mc
 var o={foo:1,a:3};o.foo+=o.a,console.log(o.foo);
 ```
 
@@ -745,8 +745,8 @@ Other options:
 ##### mangle.properties options
 
  - `regex` — Pass a RegExp to only mangle certain names
- - `ignore_quoted` – Only mangle unquoted property names
- - `debug` – Mangle names with the original name still present. Defaults to `false`.
+ - `keep_quoted` — Only mangle unquoted property names
+ - `debug` — Mangle names with the original name still present. Defaults to `false`.
    Pass an empty string to enable, or a non-empty string to set the suffix.
 
 We could add more options to `UglifyJS.minify` — if you need additional
diff --git a/lib/propmangle.js b/lib/propmangle.js
index d480d3da..efb31cc1 100644
--- a/lib/propmangle.js
+++ b/lib/propmangle.js
@@ -72,7 +72,7 @@ function mangle_properties(ast, options) {
         builtins: false,
         cache: null,
         debug: false,
-        ignore_quoted: false,
+        keep_quoted: false,
         only_cache: false,
         regex: null,
         reserved: null,
@@ -90,12 +90,12 @@ function mangle_properties(ast, options) {
     }
 
     var regex = options.regex;
-    var ignore_quoted = options.ignore_quoted;
+    var keep_quoted = options.keep_quoted;
 
     // note debug is either false (disabled), or a string of the debug suffix to use (enabled).
     // note debug may be enabled as an empty string, which is falsey. Also treat passing 'true'
     // the same as passing an empty string.
-    var debug = (options.debug !== false);
+    var debug = options.debug !== false;
     var debug_name_suffix;
     if (debug) {
         debug_name_suffix = (options.debug === true ? "" : options.debug);
@@ -103,12 +103,12 @@ function mangle_properties(ast, options) {
 
     var names_to_mangle = [];
     var unmangleable = [];
-    var ignored = {};
+    var to_keep = {};
 
     // step 1: find candidates to mangle
     ast.walk(new TreeWalker(function(node){
         if (node instanceof AST_ObjectKeyVal) {
-            add(node.key, ignore_quoted && node.quote);
+            add(node.key, keep_quoted && node.quote);
         }
         else if (node instanceof AST_ObjectProperty) {
             // setter or getter, since KeyVal is handled above
@@ -118,14 +118,14 @@ function mangle_properties(ast, options) {
             add(node.property);
         }
         else if (node instanceof AST_Sub) {
-            addStrings(node.property, ignore_quoted);
+            addStrings(node.property, keep_quoted);
         }
     }));
 
     // step 2: transform the tree, renaming properties
     return ast.transform(new TreeTransformer(function(node){
         if (node instanceof AST_ObjectKeyVal) {
-            if (!(ignore_quoted && node.quote))
+            if (!(keep_quoted && node.quote))
                 node.key = mangle(node.key);
         }
         else if (node instanceof AST_ObjectProperty) {
@@ -136,7 +136,7 @@ function mangle_properties(ast, options) {
             node.property = mangle(node.property);
         }
         else if (node instanceof AST_Sub) {
-            if (!ignore_quoted)
+            if (!keep_quoted)
                 node.property = mangleStrings(node.property);
         }
         // else if (node instanceof AST_String) {
@@ -166,16 +166,16 @@ function mangle_properties(ast, options) {
     }
 
     function should_mangle(name) {
-        if (ignore_quoted && name in ignored) return false;
+        if (keep_quoted && name in to_keep) return false;
         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;
     }
 
-    function add(name, ignore) {
-        if (ignore) {
-            ignored[name] = true;
+    function add(name, keep) {
+        if (keep) {
+            to_keep[name] = true;
             return;
         }
 
@@ -198,19 +198,19 @@ function mangle_properties(ast, options) {
                 // debug mode: use a prefix and suffix to preserve readability, e.g. o.foo -> o._$foo$NNN_.
                 var debug_mangled = "_$" + name + "$" + debug_name_suffix + "_";
 
-                if (can_mangle(debug_mangled) && !(ignore_quoted && debug_mangled in ignored)) {
+                if (can_mangle(debug_mangled) && !(keep_quoted && debug_mangled in to_keep)) {
                     mangled = debug_mangled;
                 }
             }
 
             // either debug mode is off, or it is on and we could not use the mangled name
             if (!mangled) {
-                // note can_mangle() does not check if the name collides with the 'ignored' set
-                // (filled with quoted properties when ignore_quoted set). Make sure we add this
+                // Note: `can_mangle()` does not check if the name collides with the `to_keep` set
+                // (filled with quoted properties when `keep_quoted` is set). Make sure we add this
                 // check so we don't collide with a quoted name.
                 do {
                     mangled = base54(++cache.cname);
-                } while (!can_mangle(mangled) || (ignore_quoted && mangled in ignored));
+                } while (!can_mangle(mangled) || keep_quoted && mangled in to_keep);
             }
 
             cache.props.set(name, mangled);
@@ -218,7 +218,7 @@ function mangle_properties(ast, options) {
         return mangled;
     }
 
-    function addStrings(node, ignore) {
+    function addStrings(node, keep) {
         var out = {};
         try {
             (function walk(node){
@@ -228,7 +228,7 @@ function mangle_properties(ast, options) {
                         return true;
                     }
                     if (node instanceof AST_String) {
-                        add(node.value, ignore);
+                        add(node.value, keep);
                         return true;
                     }
                     if (node instanceof AST_Conditional) {
@@ -260,5 +260,4 @@ function mangle_properties(ast, options) {
             return node;
         }));
     }
-
 }
diff --git a/test/compress/issue-1321.js b/test/compress/issue-1321.js
index 7449d3e2..dcbfde64 100644
--- a/test/compress/issue-1321.js
+++ b/test/compress/issue-1321.js
@@ -1,6 +1,6 @@
 issue_1321_no_debug: {
     mangle_props = {
-        ignore_quoted: true
+        keep_quoted: true
     }
     input: {
         var x = {};
@@ -19,7 +19,7 @@ issue_1321_no_debug: {
 
 issue_1321_debug: {
     mangle_props = {
-        ignore_quoted: true,
+        keep_quoted: true,
         debug: ""
     }
     input: {
@@ -39,7 +39,7 @@ issue_1321_debug: {
 
 issue_1321_with_quoted: {
     mangle_props = {
-        ignore_quoted: false
+        keep_quoted: false
     }
     input: {
         var x = {};
diff --git a/test/compress/properties.js b/test/compress/properties.js
index b2c201d7..3e06dc1e 100644
--- a/test/compress/properties.js
+++ b/test/compress/properties.js
@@ -125,7 +125,7 @@ evaluate_string_length: {
 
 mangle_properties: {
     mangle_props = {
-        ignore_quoted: false
+        keep_quoted: false
     };
     input: {
         a["foo"] = "bar";
@@ -148,7 +148,7 @@ mangle_unquoted_properties: {
         properties: false
     }
     mangle_props = {
-        ignore_quoted: true
+        keep_quoted: true
     }
     beautify = {
         beautify: false,
@@ -233,12 +233,12 @@ mangle_debug_suffix: {
     }
 }
 
-mangle_debug_suffix_ignore_quoted: {
+mangle_debug_suffix_keep_quoted: {
     options = {
         properties: false
     }
     mangle_props = {
-        ignore_quoted: true,
+        keep_quoted: true,
         debug: "XYZ",
         reserved: []
     }
diff --git a/test/mocha/minify.js b/test/mocha/minify.js
index e332dbef..18840a58 100644
--- a/test/mocha/minify.js
+++ b/test/mocha/minify.js
@@ -53,7 +53,7 @@ describe("minify", function() {
                 },
                 mangle: {
                     properties: {
-                        ignore_quoted: true
+                        keep_quoted: true
                     }
                 },
                 output: {