diff --git a/dev/customer_testing/lib/runner.dart b/dev/customer_testing/lib/runner.dart
index 2eec0b5ebf6..79736a77bbe 100644
--- a/dev/customer_testing/lib/runner.dart
+++ b/dev/customer_testing/lib/runner.dart
@@ -15,7 +15,7 @@ Future<bool> runTests({
   bool verbose = false,
   int numberShards = 1,
   int shardIndex = 0,
-  List<File> files,
+  required List<File> files,
 }) async {
   if (verbose)
     print('Starting run_tests.dart...');
@@ -66,7 +66,7 @@ Future<bool> runTests({
     if (verbose)
       print('Created temporary directory: ${checkout.path}');
     try {
-      bool success;
+      bool? success;
       bool showContacts = false;
       for (final String fetchCommand in instructions.fetch) {
         success = await shell(fetchCommand, checkout, verbose: verbose, silentFailure: skipOnFetchFailure);
@@ -86,7 +86,7 @@ Future<bool> runTests({
         }
       }
       assert(success != null);
-      if (success) {
+      if (success == true) {
         if (verbose)
           print('Running tests...');
         final Directory tests = Directory(path.join(checkout.path, 'tests'));
@@ -105,7 +105,7 @@ Future<bool> runTests({
             }
           }
         }
-        if (verbose && success)
+        if (verbose && success == true)
           print('Tests finished.');
       }
       if (showContacts) {
diff --git a/dev/customer_testing/pubspec.yaml b/dev/customer_testing/pubspec.yaml
index ae74de25531..e850074849f 100644
--- a/dev/customer_testing/pubspec.yaml
+++ b/dev/customer_testing/pubspec.yaml
@@ -2,7 +2,7 @@ name: customer_testing
 description: Tool to run the tests listed in the flutter/tests repository.
 
 environment:
-  sdk: '>=2.9.0 <3.0.0'
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   args: 2.0.0
diff --git a/dev/customer_testing/run_tests.dart b/dev/customer_testing/run_tests.dart
index d71ecd7dc6e..dbc2d63c6d8 100644
--- a/dev/customer_testing/run_tests.dart
+++ b/dev/customer_testing/run_tests.dart
@@ -78,13 +78,13 @@ Future<bool> run(List<String> arguments) async {
     exit(1);
   }
 
-  final int repeat = int.tryParse(parsedArguments['repeat'] as String);
+  final int? repeat = int.tryParse(parsedArguments['repeat'] as String);
   final bool skipOnFetchFailure = parsedArguments['skip-on-fetch-failure'] as bool;
   final bool skipTemplate = parsedArguments['skip-template'] as bool;
   final bool verbose = parsedArguments['verbose'] as bool;
   final bool help = parsedArguments['help'] as bool;
-  final int numberShards = int.tryParse(parsedArguments['shards'] as String);
-  final int shardIndex = int.tryParse(parsedArguments['shard-index'] as String);
+  final int? numberShards = int.tryParse(parsedArguments['shards'] as String);
+  final int? shardIndex = int.tryParse(parsedArguments['shard-index'] as String);
   final List<File> files = parsedArguments
     .rest
     .expand((String path) => Glob(path).listFileSystemSync(const LocalFileSystem()))
@@ -106,10 +106,10 @@ Future<bool> run(List<String> arguments) async {
     return help;
   }
 
-  if (files.length < shardIndex)
+  if (files.length < shardIndex!)
     print('Warning: There are more shards than tests. Some shards will not run any tests.');
 
-  if (numberShards <= shardIndex) {
+  if (numberShards! <= shardIndex) {
     print('Error: There are more shard indexes than shards.');
     return help;
   }