diff --git a/lib/parser.dart b/lib/parser.dart
index ca1f465..099240d 100644
--- a/lib/parser.dart
+++ b/lib/parser.dart
@@ -1307,12 +1307,14 @@
     var selectors = <Selector>[];
     var start = _peekToken.span;
 
+    tokenizer.inSelector = true;
     do {
       var selector = processSelector();
       if (selector != null) {
         selectors.add(selector);
       }
     } while (_maybeEat(TokenKind.COMMA));
+    tokenizer.inSelector = false;
 
     if (selectors.isNotEmpty) {
       return SelectorGroup(selectors, _makeSpan(start));
@@ -1501,35 +1503,20 @@
       case TokenKind.HASH:
         _eat(TokenKind.HASH);
 
-        var hasWhiteSpace = false;
         if (_anyWhiteSpaceBeforePeekToken(TokenKind.HASH)) {
-          _warning('Not a valid ID selector expected #id', _makeSpan(start));
-          hasWhiteSpace = true;
+          _error('Not a valid ID selector expected #id', _makeSpan(start));
+          return null;
         }
-        if (_peekIdentifier()) {
-          var id = identifier();
-          if (hasWhiteSpace) {
-            // Generate bad selector id (normalized).
-            id.name = ' ${id.name}';
-          }
-          return IdSelector(id, _makeSpan(start));
-        }
-        return null;
+        return IdSelector(identifier(), _makeSpan(start));
       case TokenKind.DOT:
         _eat(TokenKind.DOT);
 
-        var hasWhiteSpace = false;
         if (_anyWhiteSpaceBeforePeekToken(TokenKind.DOT)) {
-          _warning('Not a valid class selector expected .className',
+          _error('Not a valid class selector expected .className',
               _makeSpan(start));
-          hasWhiteSpace = true;
+          return null;
         }
-        var id = identifier();
-        if (hasWhiteSpace) {
-          // Generate bad selector class (normalized).
-          id.name = ' ${id.name}';
-        }
-        return ClassSelector(id, _makeSpan(start));
+        return ClassSelector(identifier(), _makeSpan(start));
       case TokenKind.COLON:
         // :pseudo-class ::pseudo-element
         return processPseudoSelector(start);
diff --git a/lib/src/tree.dart b/lib/src/tree.dart
index 8a17b53..2961b6f 100644
--- a/lib/src/tree.dart
+++ b/lib/src/tree.dart
@@ -20,7 +20,12 @@
   dynamic visit(VisitorBase visitor) => visitor.visitIdentifier(this);
 
   @override
-  String toString() => name;
+  String toString() {
+    // Try to use the identifier's original lexeme to preserve any escape codes
+    // as authored. The name, which may include escaped values, may no longer be
+    // a valid identifier.
+    return span?.text ?? name;
+  }
 }
 
 class Wildcard extends TreeNode {
@@ -274,7 +279,7 @@
   String valueToString() {
     if (value != null) {
       if (value is Identifier) {
-        return value.name;
+        return value.toString();
       } else {
         return '"$value"';
       }
diff --git a/test/error_test.dart b/test/error_test.dart
index d242176..5822c4c 100644
--- a/test/error_test.dart
+++ b/test/error_test.dart
@@ -134,37 +134,27 @@
 
   // Invalid id selector.
   var input = '# foo { color: #ff00ff; }';
-  var stylesheet = parseCss(input, errors: errors);
+  parseCss(input, errors: errors);
 
-  expect(errors.isEmpty, false);
+  expect(errors, isNotEmpty);
   expect(errors[0].toString(), r'''
 error on line 1, column 1: Not a valid ID selector expected #id
   ╷
 1 │ # foo { color: #ff00ff; }
   │ ^
   ╵''');
-  expect(stylesheet != null, true);
-  expect(prettyPrint(stylesheet), r'''
-# foo {
-  color: #f0f;
-}''');
 
   // Invalid class selector.
   input = '. foo { color: #ff00ff; }';
-  stylesheet = parseCss(input, errors: errors..clear());
+  parseCss(input, errors: errors..clear());
 
-  expect(errors.isEmpty, false);
+  expect(errors, isNotEmpty);
   expect(errors[0].toString(), r'''
 error on line 1, column 1: Not a valid class selector expected .className
   ╷
 1 │ . foo { color: #ff00ff; }
   │ ^
   ╵''');
-  expect(stylesheet != null, true);
-  expect(prettyPrint(stylesheet), r'''
-. foo {
-  color: #f0f;
-}''');
 }
 
 /// Test for bad hex values.
diff --git a/test/escape_codes_test.dart b/test/escape_codes_test.dart
new file mode 100644
index 0000000..af66469
--- /dev/null
+++ b/test/escape_codes_test.dart
@@ -0,0 +1,28 @@
+import 'package:csslib/parser.dart';
+import 'package:test/test.dart';
+
+import 'testing.dart';
+
+void main() {
+  final errors = <Message>[];
+
+  tearDown(() {
+    errors.clear();
+  });
+
+  group('handles escape codes', () {
+    group('in an identifier', () {
+      test('with trailing space', () {
+        final selectorAst = selector(r'.\35 00px', errors: errors);
+        expect(errors, isEmpty);
+        expect(compactOuptut(selectorAst), r'.\35 00px');
+      });
+
+      test('in an attribute selector value', () {
+        final selectorAst = selector(r'[elevation=\31]', errors: errors);
+        expect(errors, isEmpty);
+        expect(compactOuptut(selectorAst), r'[elevation=\31]');
+      });
+    });
+  });
+}