diff --git a/lib/output.js b/lib/output.js
index 9fb97c81..ccd614d3 100644
--- a/lib/output.js
+++ b/lib/output.js
@@ -115,19 +115,15 @@ function OutputStream(options) {
     var OUTPUT = "";
 
     var to_utf8 = options.ascii_only ? function(str, identifier) {
-        return str.replace(/[\ud800-\udbff][\udc00-\udfff]|[\u0000-\u001f\u007f-\uffff]/g, function(ch) {
-            var code = get_full_char_code(ch, 0).toString(16);
-
-            if ((identifier && code.length === 1 && options.ecma >= 6) || code.length > 4) {
-                if (options.ecma < 6) {
-                    if (identifier) {
-                        return ch; // no \u{} support
-                    }
-                    return "\\u" + ch.charCodeAt(0).toString(16) + "\\u"
-                        + ch.charCodeAt(1).toString(16);
-                }
+        if (options.ecma >= 6) {
+            str = str.replace(/[\ud800-\udbff][\udc00-\udfff]/g, function(ch) {
+                var code = get_full_char_code(ch, 0).toString(16);
                 return "\\u{" + code + "}";
-            } else if (code.length <= 2 && !identifier) {
+            });
+        }
+        return str.replace(/[\u0000-\u001f\u007f-\uffff]/g, function(ch) {
+            var code = ch.charCodeAt(0).toString(16);
+            if (code.length <= 2 && !identifier) {
                 while (code.length < 2) code = "0" + code;
                 return "\\x" + code;
             } else {
diff --git a/test/compress/unicode.js b/test/compress/unicode.js
index b2db1d68..d57165ea 100644
--- a/test/compress/unicode.js
+++ b/test/compress/unicode.js
@@ -43,15 +43,6 @@ unicode_string_literals: {
     expect_exact: 'var a="6 length unicode character: \\u{101111}";'
 }
 
-// Don't escape identifiers below es6 (or in this case double escaped in expect_exact)
-unicode_output_es5_surrogates: {
-    beautify = {ascii_only: true, ecma: 5}
-    input: {
-        var \u{10000} = "6 length unicode character: \u{10FFFF}";
-    }
-    expect_exact: 'var \u{10000}="6 length unicode character: \\udbff\\udfff";'
-}
-
 check_escape_style: {
     beautify = {ascii_only: true, ecma: 6}
     input: {
@@ -65,20 +56,6 @@ check_escape_style: {
     expect_exact: 'var a="\\x01";var \\ua0081="\\x10";var \\u0100="\\u0100";var \\u1000="\\u1000";var \\u{10000}="\\u{10000}";var \\u{2f800}="\\u{100000}";'
 }
 
-// Don't escape identifiers below es6, no escaped identifiers support and no \u{} syntax
-check_escape_style_es5: {
-    beautify = {ascii_only: true, ecma: 5}
-    input: {
-        var a = "\x01";
-        var \ua0081 = "\x10"; // \u0081 only in ID_Continue
-        var \u0100 = "\u0100";
-        var \u1000 = "\u1000";
-        var \u{10000} = "\u{10000}"; // Identifier won't be escaped in es 5.1
-        var \u{2f800} = "\u{100000}"; // Same
-    }
-    expect_exact: 'var a="\\x01";var \\ua0081="\\x10";var \\u0100="\\u0100";var \\u1000="\\u1000";var \ud800\udc00="\\ud800\\udc00";var \ud87e\udc00="\\udbc0\\udc00";'
-}
-
 ID_continue_with_surrogate_pair: {
     beautify = {ascii_only: true, ecma: 6}
     input: {
diff --git a/test/mocha/unicode.js b/test/mocha/unicode.js
index 37950e45..e5d94836 100644
--- a/test/mocha/unicode.js
+++ b/test/mocha/unicode.js
@@ -1,4 +1,5 @@
 var assert = require("assert");
+var semver = require("semver");
 var uglify = require("../node");
 
 describe("Unicode", function() {
@@ -138,8 +139,33 @@ describe("Unicode", function() {
 
     it("Should parse raw characters correctly", function() {
         var ast = uglify.parse('console.log("\\udbff");');
-        assert.strictEqual(ast.print_to_string(), 'console.log("\udbff");');
+        assert.strictEqual(ast.print_to_string(), 'console.log("\\udbff");');
         ast = uglify.parse(ast.print_to_string());
-        assert.strictEqual(ast.print_to_string(), 'console.log("\udbff");');
+        assert.strictEqual(ast.print_to_string(), 'console.log("\\udbff");');
     });
+
+    if (semver.satisfies(process.version, ">=4")) {
+        it("Should not unescape unpaired surrogates", function() {
+            var code = [];
+            for (var i = 0; i <= 0xFFFF; i++) {
+                code.push("\\u{" + i.toString(16) + "}");
+            }
+            code = '"' + code.join() + '"';
+            [true, false].forEach(function(ascii_only) {
+                [5, 6].forEach(function(ecma) {
+                    var result = uglify.minify(code, {
+                        compress: false,
+                        mangle: false,
+                        output: {
+                            ascii_only: ascii_only
+                        },
+                        ecma: ecma
+                    });
+                    if (result.error) throw result.error;
+                    assert.ok(code.length > result.code.length);
+                    assert.strictEqual(eval(code), eval(result.code));
+                });
+            });
+        });
+    }
 });