diff --git a/CHANGELOG.md b/CHANGELOG.md
index 37d6220..ab38339 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 2.1.1
+
+* Fix a bug with `mandatory` options which caused a null assertion failure when
+  used within a command.
+
 ## 2.1.0
 
 * Add a `mandatory` argument to require the presence of an option.
diff --git a/lib/src/parser.dart b/lib/src/parser.dart
index de987a8..ed6e2c7 100644
--- a/lib/src/parser.dart
+++ b/lib/src/parser.dart
@@ -98,7 +98,7 @@
       // Check if an option was mandatory and exist
       // if not throw an exception
       if (option.mandatory && parsedOption == null) {
-        throw ArgParserException('Option $name is mandatory.', [name]);
+        throw ArgParserException('Option $name is mandatory.');
       }
 
       var callback = option.callback;
diff --git a/pubspec.yaml b/pubspec.yaml
index 5fe2b89..e3db8cd 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: args
-version: 2.1.0
+version: 2.1.1
 homepage: https://github.com/dart-lang/args
 description: >-
  Library for defining parsers for parsing raw command-line arguments into a set
diff --git a/test/command_runner_test.dart b/test/command_runner_test.dart
index f030adc..29dd9fa 100644
--- a/test/command_runner_test.dart
+++ b/test/command_runner_test.dart
@@ -462,4 +462,30 @@
 Run "test help" to see global options.'''));
     });
   });
+
+  test('mandatory options in commands', () async {
+    var subcommand = _MandatoryOptionCommand();
+    runner.addCommand(subcommand);
+    expect(
+        () => runner.run([subcommand.name]),
+        throwsA(isA<UsageException>().having((e) => e.message, 'message',
+            contains('Option mandatory-option is mandatory'))));
+    expect(await runner.run([subcommand.name, '--mandatory-option', 'foo']),
+        'foo');
+  });
+}
+
+class _MandatoryOptionCommand extends Command {
+  _MandatoryOptionCommand() {
+    argParser.addOption('mandatory-option', mandatory: true);
+  }
+
+  @override
+  String get description => 'A command with a mandatory option';
+
+  @override
+  String get name => 'mandatory-option-command';
+
+  @override
+  String run() => argResults!['mandatory-option'];
 }