diff --git a/.github/workflows/test-package.yml b/.github/workflows/test-package.yml
index 9c89e08..b280465 100644
--- a/.github/workflows/test-package.yml
+++ b/.github/workflows/test-package.yml
@@ -47,7 +47,7 @@
       matrix:
         # Add macos-latest and/or windows-latest if relevant for this package.
         os: [ubuntu-latest]
-        sdk: [2.12.0, dev]
+        sdk: [2.18.0, dev]
     steps:
       - uses: actions/checkout@755da8c3cf115ac066823e79a1e1788f8940201b
       - uses: dart-lang/setup-dart@6a218f2413a3e78e9087f638a238f6b40893203d
diff --git a/CHANGELOG.md b/CHANGELOG.md
index b6e91bb..62ef87d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.1.1-dev
+
+- Require Dart 2.18
+
 ## 2.1.0
 
 - Adds `minVersion` to `findPackageConfig` and `findPackageConfigVersion`
diff --git a/lib/src/package_config_impl.dart b/lib/src/package_config_impl.dart
index 4c8f234..f832d6a 100644
--- a/lib/src/package_config_impl.dart
+++ b/lib/src/package_config_impl.dart
@@ -244,7 +244,7 @@
       if (!root.hasScheme) {
         fatalError = true;
       } else if (!root.path.endsWith('/')) {
-        root = root.replace(path: root.path + '/');
+        root = root.replace(path: '${root.path}/');
       }
     }
     if (packageUriRoot == null) {
diff --git a/lib/src/package_config_json.dart b/lib/src/package_config_json.dart
index fe185a2..bd22db4 100644
--- a/lib/src/package_config_json.dart
+++ b/lib/src/package_config_json.dart
@@ -149,11 +149,11 @@
     var parsedRootUri = Uri.parse(rootUri!);
     var relativeRoot = !hasAbsolutePath(parsedRootUri);
     var root = baseLocation.resolveUri(parsedRootUri);
-    if (!root.path.endsWith('/')) root = root.replace(path: root.path + '/');
+    if (!root.path.endsWith('/')) root = root.replace(path: '${root.path}/');
     var packageRoot = root;
     if (packageUri != null) packageRoot = root.resolve(packageUri!);
     if (!packageRoot.path.endsWith('/')) {
-      packageRoot = packageRoot.replace(path: packageRoot.path + '/');
+      packageRoot = packageRoot.replace(path: '${packageRoot.path}/');
     }
 
     LanguageVersion? version;
diff --git a/lib/src/packages_file.dart b/lib/src/packages_file.dart
index 2446633..3fd7db9 100644
--- a/lib/src/packages_file.dart
+++ b/lib/src/packages_file.dart
@@ -192,7 +192,7 @@
       uri = relativizeUri(uri, baseUri)!;
     }
     if (!uri.path.endsWith('/')) {
-      uri = uri.replace(path: uri.path + '/');
+      uri = uri.replace(path: '${uri.path}/');
     }
     output.write(uri);
     output.writeln();
diff --git a/lib/src/util.dart b/lib/src/util.dart
index 61488ac..3bf1bec 100644
--- a/lib/src/util.dart
+++ b/lib/src/util.dart
@@ -89,7 +89,7 @@
     }
     assert(badIndex < packageName.length);
     var badCharCode = packageName.codeUnitAt(badIndex);
-    var badChar = 'U+' + badCharCode.toRadixString(16).padLeft(4, '0');
+    var badChar = 'U+${badCharCode.toRadixString(16).padLeft(4, '0')}';
     if (badCharCode >= 0x20 && badCharCode <= 0x7e) {
       // Printable character.
       badChar = "'${packageName[badIndex]}' ($badChar)";
@@ -140,7 +140,7 @@
 /// Appends a trailing `/` if the path doesn't end with one.
 String trailingSlash(String path) {
   if (path.isEmpty || path.endsWith('/')) return path;
-  return path + '/';
+  return '$path/';
 }
 
 /// Whether a URI should not be considered relative to the base URI.
diff --git a/pubspec.yaml b/pubspec.yaml
index 56e30b5..08255ff 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,10 +1,10 @@
 name: package_config
-version: 2.1.0
+version: 2.1.1-dev
 description: Support for reading and writing Dart Package Configuration files.
 repository: https://github.com/dart-lang/package_config
 
 environment:
-  sdk: '>=2.12.0 <3.0.0'
+  sdk: '>=2.18.0 <3.0.0'
 
 dependencies:
   path: ^1.8.0
@@ -12,6 +12,6 @@
 dev_dependencies:
   build_runner: ^2.0.0
   build_test: ^2.1.2
-  build_web_compilers: ^3.0.0
-  lints: ^1.0.0
+  build_web_compilers: '>=3.0.0 <5.0.0'
+  lints: ^2.0.0
   test: ^1.16.0
diff --git a/test/parse_test.dart b/test/parse_test.dart
index 174a099..94269e2 100644
--- a/test/parse_test.dart
+++ b/test/parse_test.dart
@@ -56,7 +56,7 @@
               () => packages.parse(utf8.encode(content), baseFile, throwError),
               throwsA(TypeMatcher<FormatException>()));
         });
-        test(name + ', handle error', () {
+        test('$name, handle error', () {
           var hadError = false;
           packages.parse(utf8.encode(content), baseFile, (error) {
             hadError = true;