@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:meta/meta.dart';
 import 'package:process/process.dart';
 
 import '../base/common.dart';
@@ -17,6 +18,18 @@ import '../persistent_tool_state.dart';
 import '../runner/flutter_command.dart';
 import '../version.dart';
 
+@visibleForTesting
+String downgradePositionalArgumentErrorMessage(List<String> args) {
+  final String argString = args.join(' ');
+  final pluralized = args.length > 1 ? 'arguments' : 'argument';
+
+  return 'Unexpected positional $pluralized "$argString".\n\n'
+      '"flutter downgrade" does not support specifying a version.\n'
+      'It only undoes the last "flutter upgrade" on the current channel.\n\n'
+      'To switch to a specific Flutter version, see: '
+      'https://flutter.dev/to/switch-flutter-version';
+}
+
 /// The flutter downgrade command returns the SDK to the last recorded version
 /// for a particular branch.
 ///
@@ -80,6 +93,10 @@ class DowngradeCommand extends FlutterCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    if (argResults!.rest.isNotEmpty) {
+      throwToolExit(downgradePositionalArgumentErrorMessage(argResults!.rest), exitCode: 2);
+    }
+
     // Commands do not necessarily have access to the correct zone injected
     // values when being created. Fields must be lazily instantiated in runCommand,
     // at least until the zone injection is refactored.
 
@@ -62,6 +62,38 @@ void main() {
     );
   }, overrides: {ProcessManager: () => processManager});
 
+  for (final positionalArguments in <List<String>>[
+    <String>['3.19.0'],
+    <String>['3.19.0', 'extra'],
+    <String>['more', 'additional', 'arguments'],
+  ]) {
+    testUsingContext(
+      'Downgrade exits on unexpected positional arguments: ${positionalArguments.join(' ')}',
+      () async {
+        final fakeFlutterVersion = FakeFlutterVersion();
+        final command = DowngradeCommand(
+          persistentToolState: PersistentToolState.test(
+            directory: fileSystem.currentDirectory,
+            logger: bufferLogger,
+          ),
+          terminal: terminal,
+          stdio: stdio,
+          flutterVersion: fakeFlutterVersion,
+          logger: bufferLogger,
+        );
+
+        expect(
+          createTestCommandRunner(command).run(<String>['downgrade', ...positionalArguments]),
+          throwsToolExit(
+            message: downgradePositionalArgumentErrorMessage(positionalArguments),
+            exitCode: 2,
+          ),
+        );
+      },
+      overrides: {ProcessManager: () => processManager},
+    );
+  }
+
   testUsingContext('Downgrade exits on no recorded version', () async {
     final fakeFlutterVersion = FakeFlutterVersion(branch: 'beta');
     fileSystem.currentDirectory