diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8e572ec..a205299 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
-## 2.5.1-wip
+## 2.6.0-wip
 
+* Added source argument when throwing a `ArgParserException`.
+* Fix inconsistent `FormatException` messages
 * Require Dart 3.3
 
 ## 2.5.0
diff --git a/lib/src/arg_parser_exception.dart b/lib/src/arg_parser_exception.dart
index d727d70..fbee82b 100644
--- a/lib/src/arg_parser_exception.dart
+++ b/lib/src/arg_parser_exception.dart
@@ -9,6 +9,14 @@ class ArgParserException extends FormatException {
   /// This will be empty if the error was on the root parser.
   final List<String> commands;
 
-  ArgParserException(super.message, [Iterable<String>? commands])
+  /// The name of the argument that was being parsed when the error was
+  /// discovered.
+  final String? argumentName;
+
+  ArgParserException(super.message,
+      [Iterable<String>? commands,
+      this.argumentName,
+      super.source,
+      super.offset])
       : commands = commands == null ? const [] : List.unmodifiable(commands);
 }
diff --git a/lib/src/arg_results.dart b/lib/src/arg_results.dart
index 9fa87cd..72c4410 100644
--- a/lib/src/arg_results.dart
+++ b/lib/src/arg_results.dart
@@ -66,7 +66,7 @@ class ArgResults {
   /// > flags, [option] for options, and [multiOption] for multi-options.
   dynamic operator [](String name) {
     if (!_parser.options.containsKey(name)) {
-      throw ArgumentError('Could not find an option named "$name".');
+      throw ArgumentError('Could not find an option named "--$name".');
     }
 
     final option = _parser.options[name]!;
@@ -83,7 +83,7 @@ class ArgResults {
   bool flag(String name) {
     var option = _parser.options[name];
     if (option == null) {
-      throw ArgumentError('Could not find an option named "$name".');
+      throw ArgumentError('Could not find an option named "--$name".');
     }
     if (!option.isFlag) {
       throw ArgumentError('"$name" is not a flag.');
@@ -97,7 +97,7 @@ class ArgResults {
   String? option(String name) {
     var option = _parser.options[name];
     if (option == null) {
-      throw ArgumentError('Could not find an option named "$name".');
+      throw ArgumentError('Could not find an option named "--$name".');
     }
     if (!option.isSingle) {
       throw ArgumentError('"$name" is a multi-option.');
@@ -111,7 +111,7 @@ class ArgResults {
   List<String> multiOption(String name) {
     var option = _parser.options[name];
     if (option == null) {
-      throw ArgumentError('Could not find an option named "$name".');
+      throw ArgumentError('Could not find an option named "--$name".');
     }
     if (!option.isMultiple) {
       throw ArgumentError('"$name" is not a multi-option.');
@@ -143,7 +143,7 @@ class ArgResults {
   /// [name] must be a valid option name in the parser.
   bool wasParsed(String name) {
     if (!_parser.options.containsKey(name)) {
-      throw ArgumentError('Could not find an option named "$name".');
+      throw ArgumentError('Could not find an option named "--$name".');
     }
 
     return _parsed.containsKey(name);
diff --git a/lib/src/parser.dart b/lib/src/parser.dart
index 3c5dfed..660e56d 100644
--- a/lib/src/parser.dart
+++ b/lib/src/parser.dart
@@ -63,7 +63,8 @@ class Parser {
       // options so that commands can have option-like names.
       var command = _grammar.commands[_current];
       if (command != null) {
-        _validate(_rest.isEmpty, 'Cannot specify arguments before a command.');
+        _validate(_rest.isEmpty, 'Cannot specify arguments before a command.',
+            _current);
         var commandName = _args.removeFirst();
         var commandParser = Parser(commandName, command, _args, this, _rest);
 
@@ -71,7 +72,11 @@ class Parser {
           commandResults = commandParser.parse();
         } on ArgParserException catch (error) {
           throw ArgParserException(
-              error.message, [commandName, ...error.commands]);
+              error.message,
+              [commandName, ...error.commands],
+              error.argumentName,
+              error.source,
+              error.offset);
         }
 
         // All remaining arguments were passed to command so clear them here.
@@ -101,7 +106,7 @@ class Parser {
       // Check if an option is mandatory and was passed; if not, throw an
       // exception.
       if (option.mandatory && parsedOption == null) {
-        throw ArgParserException('Option $name is mandatory.');
+        throw ArgParserException('Option $name is mandatory.', null, name);
       }
 
       // ignore: avoid_dynamic_calls
@@ -118,11 +123,11 @@ class Parser {
   /// Pulls the value for [option] from the second argument in [_args].
   ///
   /// Validates that there is a valid value there.
-  void _readNextArgAsValue(Option option) {
+  void _readNextArgAsValue(Option option, String arg) {
     // Take the option argument from the next command line arg.
-    _validate(_args.isNotEmpty, 'Missing argument for "${option.name}".');
+    _validate(_args.isNotEmpty, 'Missing argument for "$arg".', arg);
 
-    _setOption(_results, option, _current);
+    _setOption(_results, option, _current, arg);
     _args.removeFirst();
   }
 
@@ -145,7 +150,8 @@ class Parser {
     var option = _grammar.findByAbbreviation(opt);
     if (option == null) {
       // Walk up to the parent command if possible.
-      _validate(_parent != null, 'Could not find an option or flag "-$opt".');
+      _validate(_parent != null, 'Could not find an option or flag "-$opt".',
+          '-$opt');
       return _parent!._handleSoloOption(opt);
     }
 
@@ -154,7 +160,7 @@ class Parser {
     if (option.isFlag) {
       _setFlag(_results, option, true);
     } else {
-      _readNextArgAsValue(option);
+      _readNextArgAsValue(option, '-$opt');
     }
 
     return true;
@@ -193,22 +199,23 @@ class Parser {
     var first = _grammar.findByAbbreviation(c);
     if (first == null) {
       // Walk up to the parent command if possible.
-      _validate(
-          _parent != null, 'Could not find an option with short name "-$c".');
+      _validate(_parent != null,
+          'Could not find an option with short name "-$c".', '-$c');
       return _parent!
           ._handleAbbreviation(lettersAndDigits, rest, innermostCommand);
     } else if (!first.isFlag) {
       // The first character is a non-flag option, so the rest must be the
       // value.
       var value = '${lettersAndDigits.substring(1)}$rest';
-      _setOption(_results, first, value);
+      _setOption(_results, first, value, '-$c');
     } else {
       // If we got some non-flag characters, then it must be a value, but
       // if we got here, it's a flag, which is wrong.
       _validate(
           rest == '',
           'Option "-$c" is a flag and cannot handle value '
-          '"${lettersAndDigits.substring(1)}$rest".');
+              '"${lettersAndDigits.substring(1)}$rest".',
+          '-$c');
 
       // Not an option, so all characters should be flags.
       // We use "innermostCommand" here so that if a parent command parses the
@@ -228,16 +235,16 @@ class Parser {
     var option = _grammar.findByAbbreviation(c);
     if (option == null) {
       // Walk up to the parent command if possible.
-      _validate(
-          _parent != null, 'Could not find an option with short name "-$c".');
+      _validate(_parent != null,
+          'Could not find an option with short name "-$c".', '-$c');
       _parent!._parseShortFlag(c);
       return;
     }
 
     // In a list of short options, only the first can be a non-flag. If
     // we get here we've checked that already.
-    _validate(
-        option.isFlag, 'Option "-$c" must be a flag to be in a collapsed "-".');
+    _validate(option.isFlag,
+        'Option "-$c" must be a flag to be in a collapsed "-".', '-$c');
 
     _setFlag(_results, option, true);
   }
@@ -269,16 +276,16 @@ class Parser {
     if (option != null) {
       _args.removeFirst();
       if (option.isFlag) {
-        _validate(
-            value == null, 'Flag option "$name" should not be given a value.');
+        _validate(value == null,
+            'Flag option "--$name" should not be given a value.', '--$name');
 
         _setFlag(_results, option, true);
       } else if (value != null) {
         // We have a value like --foo=bar.
-        _setOption(_results, option, value);
+        _setOption(_results, option, value, '--$name');
       } else {
         // Option like --foo, so look for the value as the next arg.
-        _readNextArgAsValue(option);
+        _readNextArgAsValue(option, '--$name');
       }
     } else if (name.startsWith('no-')) {
       // See if it's a negated flag.
@@ -286,18 +293,22 @@ class Parser {
       option = _grammar.findByNameOrAlias(positiveName);
       if (option == null) {
         // Walk up to the parent command if possible.
-        _validate(_parent != null, 'Could not find an option named "$name".');
+        _validate(_parent != null, 'Could not find an option named "--$name".',
+            '--$name');
         return _parent!._handleLongOption(name, value);
       }
 
       _args.removeFirst();
-      _validate(option.isFlag, 'Cannot negate non-flag option "$name".');
-      _validate(option.negatable!, 'Cannot negate option "$name".');
+      _validate(
+          option.isFlag, 'Cannot negate non-flag option "--$name".', '--$name');
+      _validate(
+          option.negatable!, 'Cannot negate option "--$name".', '--$name');
 
       _setFlag(_results, option, false);
     } else {
       // Walk up to the parent command if possible.
-      _validate(_parent != null, 'Could not find an option named "$name".');
+      _validate(_parent != null, 'Could not find an option named "--$name".',
+          '--$name');
       return _parent!._handleLongOption(name, value);
     }
 
@@ -307,17 +318,20 @@ class Parser {
   /// Called during parsing to validate the arguments.
   ///
   /// Throws an [ArgParserException] if [condition] is `false`.
-  void _validate(bool condition, String message) {
-    if (!condition) throw ArgParserException(message);
+  void _validate(bool condition, String message,
+      [String? args, List<String>? source, int? offset]) {
+    if (!condition) {
+      throw ArgParserException(message, null, args, source, offset);
+    }
   }
 
   /// Validates and stores [value] as the value for [option], which must not be
   /// a flag.
-  void _setOption(Map results, Option option, String value) {
+  void _setOption(Map results, Option option, String value, String arg) {
     assert(!option.isFlag);
 
     if (!option.isMultiple) {
-      _validateAllowed(option, value);
+      _validateAllowed(option, value, arg);
       results[option.name] = value;
       return;
     }
@@ -326,11 +340,11 @@ class Parser {
 
     if (option.splitCommas) {
       for (var element in value.split(',')) {
-        _validateAllowed(option, element);
+        _validateAllowed(option, element, arg);
         list.add(element);
       }
     } else {
-      _validateAllowed(option, value);
+      _validateAllowed(option, value, arg);
       list.add(value);
     }
   }
@@ -343,11 +357,11 @@ class Parser {
   }
 
   /// Validates that [value] is allowed as a value of [option].
-  void _validateAllowed(Option option, String value) {
+  void _validateAllowed(Option option, String value, String arg) {
     if (option.allowed == null) return;
 
     _validate(option.allowed!.contains(value),
-        '"$value" is not an allowed value for option "${option.name}".');
+        '"$value" is not an allowed value for option "$arg".', arg);
   }
 }
 
diff --git a/pubspec.yaml b/pubspec.yaml
index 2b70992..8e59181 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: args
-version: 2.5.1-wip
+version: 2.6.0-wip
 description: >-
   Library for defining parsers for parsing raw command-line arguments into a set
   of options and values using GNU and POSIX style options.
diff --git a/test/command_runner_test.dart b/test/command_runner_test.dart
index cc80c6b..b9fde8a 100644
--- a/test/command_runner_test.dart
+++ b/test/command_runner_test.dart
@@ -583,7 +583,7 @@ Run "test help" to see global options.
         expect(
             runner.run(['--asdf']),
             throwsUsageException(
-                'Could not find an option named "asdf".', _defaultUsage));
+                'Could not find an option named "--asdf".', _defaultUsage));
       });
 
       test('for a command throws the command usage', () {
@@ -591,7 +591,7 @@ Run "test help" to see global options.
         runner.addCommand(command);
 
         expect(runner.run(['foo', '--asdf']),
-            throwsUsageException('Could not find an option named "asdf".', '''
+            throwsUsageException('Could not find an option named "--asdf".', '''
 Usage: test foo [arguments]
 -h, --help    Print this usage information.
 
@@ -616,7 +616,7 @@ Also, footer!'''));
     test('includes the footer in usage errors', () {
       expect(
           runner.run(['--bad']),
-          throwsUsageException('Could not find an option named "bad".',
+          throwsUsageException('Could not find an option named "--bad".',
               '$_defaultUsage\nAlso, footer!'));
     });
   });
@@ -652,7 +652,7 @@ newlines properly.'''));
 
     test('includes the footer in usage errors', () {
       expect(runner.run(['--bad']),
-          throwsUsageException('Could not find an option named "bad".', '''
+          throwsUsageException('Could not find an option named "--bad".', '''
 Usage: test <command> [arguments]
 
 Global options:
@@ -679,7 +679,7 @@ newlines properly.'''));
       expect(
           runner.run(['--bad']),
           throwsUsageException(
-              'Could not find an option named "bad".', _defaultUsage));
+              'Could not find an option named "--bad".', _defaultUsage));
     });
 
     test("a top-level command doesn't exist", () {
diff --git a/test/parse_test.dart b/test/parse_test.dart
index b2dda44..9501b5d 100644
--- a/test/parse_test.dart
+++ b/test/parse_test.dart
@@ -766,5 +766,54 @@ void main() {
         expect(results.rest, equals(['stop', '--', 'arg']));
       });
     });
+
+    group('ArgParser Exception Tests', () {
+      test('throws exception for unknown option', () {
+        var parser = ArgParser();
+        throwsArgParserException(parser, ['--verbose'],
+            'Could not find an option named "--verbose".', [], '--verbose');
+        throwsArgParserException(
+            parser, ['-v'], 'Could not find an option or flag "-v".', [], '-v');
+      });
+
+      test('throws exception for flag with value', () {
+        var parser = ArgParser();
+        parser.addFlag('flag', abbr: 'f');
+        throwsArgParserException(parser, ['--flag=1'],
+            'Flag option "--flag" should not be given a value.', [], '--flag');
+        throwsArgParserException(parser, ['-f=1'],
+            'Option "-f" is a flag and cannot handle value "=1".', [], '-f');
+      });
+
+      test('throws exception after parsing multiple options', () {
+        var parser = ArgParser();
+        parser.addOption('first');
+        parser.addOption('second');
+        throwsArgParserException(
+            parser,
+            ['--first', '1', '--second', '2', '--verbose', '3'],
+            'Could not find an option named "--verbose".',
+            [],
+            '--verbose');
+      });
+
+      test('throws exception for option with invalid value', () {
+        var parser = ArgParser();
+        parser.addOption('first', allowed: ['a', 'b']);
+        throwsArgParserException(parser, ['--first', 'c'],
+            '"c" is not an allowed value for option "--first".', [], '--first');
+      });
+
+      test('throws exception after parsing command', () {
+        var parser = ArgParser();
+        parser.addCommand('command', ArgParser());
+        throwsArgParserException(
+            parser,
+            ['command', '--verbose'],
+            'Could not find an option named "--verbose".',
+            ['command'],
+            '--verbose');
+      });
+    });
   });
 }
diff --git a/test/test_utils.dart b/test/test_utils.dart
index f19da6d..f7d8b8a 100644
--- a/test/test_utils.dart
+++ b/test/test_utils.dart
@@ -343,8 +343,23 @@ void throwsIllegalArg(void Function() function, {String? reason}) {
   expect(function, throwsArgumentError, reason: reason);
 }
 
-void throwsFormat(ArgParser parser, List<String> args) {
-  expect(() => parser.parse(args), throwsFormatException);
+void throwsFormat(ArgParser parser, List<String> args, {String? reason}) {
+  expect(() => parser.parse(args), throwsA(isA<FormatException>()),
+      reason: reason);
+}
+
+void throwsArgParserException(ArgParser parser, List<String> args,
+    String message, List<String> commands, String arg) {
+  try {
+    parser.parse(args);
+    fail('Expected an ArgParserException');
+  } on ArgParserException catch (e) {
+    expect(e.message, message);
+    expect(e.commands, commands);
+    expect(e.argumentName, arg);
+  } catch (e) {
+    fail('Expected an ArgParserException, but got $e');
+  }
 }
 
 Matcher throwsUsageException(Object? message, Object? usage) =>
diff --git a/test/trailing_options_test.dart b/test/trailing_options_test.dart
index 505b6b1..db502d1 100644
--- a/test/trailing_options_test.dart
+++ b/test/trailing_options_test.dart
@@ -5,6 +5,8 @@
 import 'package:args/args.dart';
 import 'package:test/test.dart';
 
+import 'test_utils.dart';
+
 void main() {
   test('allowTrailingOptions defaults to true', () {
     var parser = ArgParser();
@@ -17,9 +19,8 @@ void main() {
       parser = ArgParser(allowTrailingOptions: true);
     });
 
-    void expectThrows(List<String> args) {
-      expect(() => parser.parse(args), throwsFormatException,
-          reason: 'with allowTrailingOptions: true');
+    void expectThrows(List<String> args, String arg) {
+      throwsFormat(parser, args, reason: 'with allowTrailingOptions: true');
     }
 
     test('collects non-options in rest', () {
@@ -56,7 +57,7 @@ void main() {
 
     test('throws on a trailing option missing its value', () {
       parser.addOption('opt');
-      expectThrows(['arg', '--opt']);
+      expectThrows(['arg', '--opt'], '--opt');
     });
 
     test('parses a trailing option', () {
@@ -67,16 +68,16 @@ void main() {
     });
 
     test('throws on a trailing unknown flag', () {
-      expectThrows(['arg', '--xflag']);
+      expectThrows(['arg', '--xflag'], '--xflag');
     });
 
     test('throws on a trailing unknown option and value', () {
-      expectThrows(['arg', '--xopt', 'v']);
+      expectThrows(['arg', '--xopt', 'v'], '--xopt');
     });
 
     test('throws on a command', () {
       parser.addCommand('com');
-      expectThrows(['arg', 'com']);
+      expectThrows(['arg', 'com'], 'com');
     });
   });