diff --git a/packages/combinator/CHANGELOG.md b/packages/combinator/CHANGELOG.md
index 3a6bcd0..01f140d 100644
--- a/packages/combinator/CHANGELOG.md
+++ b/packages/combinator/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Change Log
 
+## 4.0.0
+
+* Require Dart >= 2.17
+
 ## 3.0.1
 
 * Fixed license link
diff --git a/packages/combinator/lib/src/combinator/chain.dart b/packages/combinator/lib/src/combinator/chain.dart
index 101836b..5833323 100644
--- a/packages/combinator/lib/src/combinator/chain.dart
+++ b/packages/combinator/lib/src/combinator/chain.dart
@@ -62,7 +62,7 @@ class _Chain<T> extends ListParser<T> {
       }
 
       if (result.value != null) {
-        results.add(result.value!);
+        results.add(result.value as T);
       } else {
         results.add('NULL' as T);
       }
diff --git a/packages/combinator/lib/src/combinator/check.dart b/packages/combinator/lib/src/combinator/check.dart
index a6f7bed..3ef6652 100644
--- a/packages/combinator/lib/src/combinator/check.dart
+++ b/packages/combinator/lib/src/combinator/check.dart
@@ -19,7 +19,7 @@ class _Check<T> extends Parser<T> {
         SyntaxError(
           severity,
           errorMessage ??
-              matcher.describe(StringDescription('Expected ')).toString() + '.',
+              '${matcher.describe(StringDescription('Expected '))}.',
           result.span,
         ),
       ]);
diff --git a/packages/combinator/lib/src/combinator/repeat.dart b/packages/combinator/lib/src/combinator/repeat.dart
index 3e159ad..6b89019 100644
--- a/packages/combinator/lib/src/combinator/repeat.dart
+++ b/packages/combinator/lib/src/combinator/repeat.dart
@@ -25,7 +25,7 @@ class _Repeat<T> extends ListParser<T> {
       if (result.successful) {
         success++;
         if (result.value != null) {
-          results.add(result.value!);
+          results.add(result.value as T);
         }
         replay = args.scanner.position;
       } else if (backtrack) {
diff --git a/packages/combinator/lib/src/combinator/to_list.dart b/packages/combinator/lib/src/combinator/to_list.dart
index 320be1f..bfd7e7b 100644
--- a/packages/combinator/lib/src/combinator/to_list.dart
+++ b/packages/combinator/lib/src/combinator/to_list.dart
@@ -15,7 +15,7 @@ class _ToList<T> extends ListParser<T> {
 
     var values = <T>[];
     if (result.value != null) {
-      values.add(result.value!);
+      values.add(result.value as T);
     }
     return ParseResult(
       args.trampoline,
diff --git a/packages/combinator/pubspec.yaml b/packages/combinator/pubspec.yaml
index 01d5b1f..c56b08a 100644
--- a/packages/combinator/pubspec.yaml
+++ b/packages/combinator/pubspec.yaml
@@ -1,15 +1,15 @@
 name: belatuk_combinator
-version: 3.0.1
+version: 4.0.0
 description: Packrat parser combinators that support static typing, generics, file spans, memoization, and more.
 homepage: https://github.com/dart-backend/belatuk-common-utilities/tree/main/packages/combinator
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: '>=2.17.0 <3.0.0'
 dependencies:
-  belatuk_code_buffer: ^3.0.0
+  belatuk_code_buffer: ^4.0.0
   matcher: ^0.12.10
   source_span: ^1.8.1
   string_scanner: ^1.1.0
   tuple: ^2.0.0
 dev_dependencies:
   test: ^1.17.4
-  lints: ^1.0.0
+  lints: ^2.0.0
diff --git a/packages/combinator/test/misc_test.dart b/packages/combinator/test/misc_test.dart
index 1487824..9d3f734 100644
--- a/packages/combinator/test/misc_test.dart
+++ b/packages/combinator/test/misc_test.dart
@@ -1,5 +1,4 @@
 import 'package:belatuk_combinator/belatuk_combinator.dart';
-import 'package:matcher/matcher.dart';
 import 'package:test/test.dart';
 import 'common.dart';