diff --git a/lib/src/enums/sentinel.dart b/lib/src/enums/sentinel.dart
new file mode 100644
index 0000000..ce4af15
--- /dev/null
+++ b/lib/src/enums/sentinel.dart
@@ -0,0 +1,29 @@
+enum Sentinel {
+  /// This is what browsers will submit when the ✓ character occurs in an
+  /// application/x-www-form-urlencoded body and the encoding of the page containing
+  /// the form is iso-8859-1, or when the submitted form has an accept-charset
+  /// attribute of iso-8859-1. Presumably also with other charsets that do not contain
+  /// the ✓ character, such as us-ascii.
+  iso(
+    value: r'✓',
+    encoded: r'utf8=%26%2310003%3B',
+  ),
+
+  /// These are the percent-encoded utf-8 octets representing a checkmark,
+  /// indicating that the request actually is utf-8 encoded.
+  charset(
+    value: r'✓',
+    encoded: r'utf8=%E2%9C%93',
+  );
+
+  const Sentinel({
+    required this.value,
+    required this.encoded,
+  });
+
+  final String value;
+  final String encoded;
+
+  @override
+  String toString() => encoded;
+}
diff --git a/lib/src/extensions/decode.dart b/lib/src/extensions/decode.dart
index 0b0926a..65dc0e6 100644
--- a/lib/src/extensions/decode.dart
+++ b/lib/src/extensions/decode.dart
@@ -35,9 +35,9 @@ extension _$Decode on QS {
     if (options.charsetSentinel) {
       for (i = 0; i < parts.length; ++i) {
         if (parts.elementAt(i).startsWith('utf8=')) {
-          if (parts.elementAt(i) == Utils.charsetSentinel) {
+          if (parts.elementAt(i) == Sentinel.charset.toString()) {
             charset = utf8;
-          } else if (parts.elementAt(i) == Utils.isoSentinel) {
+          } else if (parts.elementAt(i) == Sentinel.iso.toString()) {
             charset = latin1;
           }
           skipIndex = i;
diff --git a/lib/src/qs.dart b/lib/src/qs.dart
index 39bbc96..db8eca6 100644
--- a/lib/src/qs.dart
+++ b/lib/src/qs.dart
@@ -4,6 +4,7 @@ import 'dart:typed_data';
 import 'package:qs_dart/src/enums/duplicates.dart';
 import 'package:qs_dart/src/enums/format.dart';
 import 'package:qs_dart/src/enums/list_format.dart';
+import 'package:qs_dart/src/enums/sentinel.dart';
 import 'package:qs_dart/src/models/decode_options.dart';
 import 'package:qs_dart/src/models/encode_options.dart';
 import 'package:qs_dart/src/models/undefined.dart';
@@ -11,6 +12,7 @@ import 'package:qs_dart/src/utils.dart';
 import 'package:weak_map/weak_map.dart';
 
 part 'extensions/decode.dart';
+
 part 'extensions/encode.dart';
 
 final class QS {
@@ -139,10 +141,10 @@ final class QS {
       if (options.charset == latin1) {
         /// encodeURIComponent('&#10003;')
         /// the "numeric entity" representation of a checkmark
-        prefix += '${Utils.isoSentinel}&';
+        prefix += '${Sentinel.iso}&';
       } else if (options.charset == utf8) {
         /// encodeURIComponent('✓')
-        prefix += '${Utils.charsetSentinel}&';
+        prefix += '${Sentinel.charset}&';
       } else {
         throw ArgumentError.value(
           options.charset,
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index 0429c83..b1979e6 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -12,17 +12,6 @@ import 'package:qs_dart/src/models/undefined.dart';
 part 'constants/hex_table.dart';
 
 final class Utils {
-  static void compactQueue(List<Map> queue) {
-    while (queue.length > 1) {
-      final Map item = queue.removeLast();
-      final dynamic obj = item['obj'][item['prop']];
-
-      if (obj is List) {
-        item['obj'][item['prop']] = obj.whereNotUndefined();
-      }
-    }
-  }
-
   static dynamic merge(
     dynamic target,
     dynamic source, [
@@ -361,13 +350,24 @@ final class Utils {
       }
     }
 
-    compactQueue(queue);
+    _compactQueue(queue);
 
     removeUndefinedFromMap(value);
 
     return value;
   }
 
+  static void _compactQueue(List<Map> queue) {
+    while (queue.length > 1) {
+      final Map item = queue.removeLast();
+      final dynamic obj = item['obj'][item['prop']];
+
+      if (obj is List) {
+        item['obj'][item['prop']] = obj.whereNotUndefined();
+      }
+    }
+  }
+
   @visibleForTesting
   static void removeUndefinedFromList(dynamic value) {
     if (value is List) {
@@ -429,17 +429,4 @@ final class Utils {
       (val is String && val.isEmpty) ||
       (val is Iterable && val.isEmpty) ||
       (val is Map && val.isEmpty);
-
-  /// This is what browsers will submit when the ✓ character occurs in an
-  /// application/x-www-form-urlencoded body and the encoding of the page containing
-  /// the form is iso-8859-1, or when the submitted form has an accept-charset
-  /// attribute of iso-8859-1. Presumably also with other charsets that do not contain
-  /// the ✓ character, such as us-ascii.
-  static const String isoSentinel =
-      r'utf8=%26%2310003%3B'; // encodeURIComponent('&#10003;')
-
-  /// These are the percent-encoded utf-8 octets representing a checkmark,
-  /// indicating that the request actually is utf-8 encoded.
-  static const String charsetSentinel =
-      r'utf8=%E2%9C%93'; // encodeURIComponent('✓')
 }