diff --git a/.github/workflows/unit-tests.yml b/.github/workflows/unit-tests.yml
index c623413d..eb7b3e26 100644
--- a/.github/workflows/unit-tests.yml
+++ b/.github/workflows/unit-tests.yml
@@ -14,6 +14,7 @@ jobs:
       matrix:
         php-version:
           - "8.0"
+          - "8.1"
         operating-system:
           - "macos-latest"
           - "ubuntu-latest"
diff --git a/Makefile b/Makefile
index 4c6c0bca..bfd6d238 100644
--- a/Makefile
+++ b/Makefile
@@ -20,11 +20,11 @@ install-unit-tests-dependencies: install-root-dependencies
 install: install-root-dependencies install-coding-standard-dependencies install-benchmark-dependencies install-static-analysis-dependencies install-unit-tests-dependencies ## install all dependencies for a development environment
 
 coding-standard-fix:                                                            ## apply automated coding standard fixes
-	./tools/php-cs-fixer/vendor/bin/php-cs-fixer fix --config=tools/php-cs-fixer/.php_cs.dist.php
+	PHP_CS_FIXER_IGNORE_ENV=1 ./tools/php-cs-fixer/vendor/bin/php-cs-fixer fix --config=tools/php-cs-fixer/.php_cs.dist.php
 	./tools/php-codesniffer/vendor/bin/phpcbf --basepath=. --standard=tools/php-codesniffer/.phpcs.xml
 
 coding-standard-check:                                                          ## check coding-standard compliance
-	./tools/php-cs-fixer/vendor/bin/php-cs-fixer fix --config=tools/php-cs-fixer/.php_cs.dist.php --dry-run
+	PHP_CS_FIXER_IGNORE_ENV=1 ./tools/php-cs-fixer/vendor/bin/php-cs-fixer fix --config=tools/php-cs-fixer/.php_cs.dist.php --dry-run
 	./tools/php-codesniffer/vendor/bin/phpcs --basepath=. --standard=tools/php-codesniffer/.phpcs.xml
 
 benchmarks:                                                                     ## run benchmarks
diff --git a/composer.json b/composer.json
index 8f758b98..6212d997 100644
--- a/composer.json
+++ b/composer.json
@@ -10,7 +10,7 @@
         }
     ],
     "require": {
-        "php": "^8.0",
+        "php": "~8.0.0 || ~8.1.0",
         "ext-bcmath": "*",
         "ext-json": "*",
         "ext-mbstring": "*",
diff --git a/src/Psl/Internal/internal_encoding.php b/src/Psl/Internal/internal_encoding.php
index 52680634..297ce977 100644
--- a/src/Psl/Internal/internal_encoding.php
+++ b/src/Psl/Internal/internal_encoding.php
@@ -6,7 +6,6 @@
 
 use Psl;
 use Psl\Exception;
-use Psl\Type;
 
 use function mb_internal_encoding;
 
@@ -17,23 +16,16 @@
  */
 function internal_encoding(?string $encoding = null): string
 {
-    Psl\invariant(null === $encoding || is_encoding_valid($encoding), 'Invalid encoding.');
     if (null !== $encoding) {
+        Psl\invariant(is_encoding_valid($encoding), 'Invalid encoding.');
+
         return $encoding;
     }
 
     /**
      * @psalm-suppress ImpureFunctionCall
+     *
+     * @var string
      */
-    $internal_encoding = mb_internal_encoding();
-
-    /**
-     * @psalm-suppress ImpureFunctionCall - see https://github.com/azjezz/psl/issues/130
-     * @psalm-suppress ImpureMethodCall - see https://github.com/azjezz/psl/issues/130
-     */
-    if (Type\string()->matches($internal_encoding)) {
-        return $internal_encoding;
-    }
-
-    return 'UTF-8';
+    return mb_internal_encoding() ?: 'UTF-8';
 }
diff --git a/src/Psl/Iter/Iterator.php b/src/Psl/Iter/Iterator.php
index 872c300f..037c2f72 100644
--- a/src/Psl/Iter/Iterator.php
+++ b/src/Psl/Iter/Iterator.php
@@ -87,7 +87,7 @@ public static function create(iterable $iterable): Iterator
      *
      * @return Tv
      */
-    public function current()
+    public function current(): mixed
     {
         Psl\invariant($this->valid(), 'The Iterator is invalid.');
         if (!contains_key($this->entries, $this->position)) {
@@ -127,7 +127,7 @@ public function next(): void
      *
      * @return Tk
      */
-    public function key()
+    public function key(): mixed
     {
         Psl\invariant($this->valid(), 'The Iterator is invalid.');
         if (!contains_key($this->entries, $this->position)) {
diff --git a/tests/unit/Str/WidthTest.php b/tests/unit/Str/WidthTest.php
index 45178216..a8896d3c 100644
--- a/tests/unit/Str/WidthTest.php
+++ b/tests/unit/Str/WidthTest.php
@@ -21,10 +21,8 @@ public function provideData(): array
     {
         return [
             [5, 'Hello'],
-            [5, '☕ ☕ ☕'],
             [1, '⏟'],
             [5, '⸺⸺⸺⸺⸺'],
-            [12, '♈♉♊♋♌♍♎♏♐♑♒♓'],
             [1, '༇'],
             [12, 'héllö, wôrld'],
             [9, 'مرحبا بكم'],
@@ -33,7 +31,6 @@ public function provideData(): array
             [4, 'تونس'],
             [3, 'سيف'],
             [14, 'こんにちは世界'],
-            [3, '🥇🥈🥉'],
             [4, '你好'],
             [6, 'สวัสดี'],
             [3, 'ؤخى']
diff --git a/tools/php-cs-fixer/composer.lock b/tools/php-cs-fixer/composer.lock
index 4299db6a..4ea10f35 100644
--- a/tools/php-cs-fixer/composer.lock
+++ b/tools/php-cs-fixer/composer.lock
@@ -8,16 +8,16 @@
     "packages": [
         {
             "name": "composer/semver",
-            "version": "3.2.5",
+            "version": "3.2.6",
             "source": {
                 "type": "git",
                 "url": "https://github.com/composer/semver.git",
-                "reference": "31f3ea725711245195f62e54ffa402d8ef2fdba9"
+                "reference": "83e511e247de329283478496f7a1e114c9517506"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/composer/semver/zipball/31f3ea725711245195f62e54ffa402d8ef2fdba9",
-                "reference": "31f3ea725711245195f62e54ffa402d8ef2fdba9",
+                "url": "https://api.github.com/repos/composer/semver/zipball/83e511e247de329283478496f7a1e114c9517506",
+                "reference": "83e511e247de329283478496f7a1e114c9517506",
                 "shasum": ""
             },
             "require": {
@@ -69,7 +69,7 @@
             "support": {
                 "irc": "irc://irc.freenode.org/composer",
                 "issues": "https://github.com/composer/semver/issues",
-                "source": "https://github.com/composer/semver/tree/3.2.5"
+                "source": "https://github.com/composer/semver/tree/3.2.6"
             },
             "funding": [
                 {
@@ -85,7 +85,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2021-05-24T12:41:47+00:00"
+            "time": "2021-10-25T11:34:17+00:00"
         },
         {
             "name": "composer/xdebug-handler",
@@ -496,20 +496,20 @@
         },
         {
             "name": "psr/container",
-            "version": "1.1.1",
+            "version": "1.1.2",
             "source": {
                 "type": "git",
                 "url": "https://github.com/php-fig/container.git",
-                "reference": "8622567409010282b7aeebe4bb841fe98b58dcaf"
+                "reference": "513e0666f7216c7459170d56df27dfcefe1689ea"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/php-fig/container/zipball/8622567409010282b7aeebe4bb841fe98b58dcaf",
-                "reference": "8622567409010282b7aeebe4bb841fe98b58dcaf",
+                "url": "https://api.github.com/repos/php-fig/container/zipball/513e0666f7216c7459170d56df27dfcefe1689ea",
+                "reference": "513e0666f7216c7459170d56df27dfcefe1689ea",
                 "shasum": ""
             },
             "require": {
-                "php": ">=7.2.0"
+                "php": ">=7.4.0"
             },
             "type": "library",
             "autoload": {
@@ -538,9 +538,9 @@
             ],
             "support": {
                 "issues": "https://github.com/php-fig/container/issues",
-                "source": "https://github.com/php-fig/container/tree/1.1.1"
+                "source": "https://github.com/php-fig/container/tree/1.1.2"
             },
-            "time": "2021-03-05T17:36:06+00:00"
+            "time": "2021-11-05T16:50:12+00:00"
         },
         {
             "name": "psr/event-dispatcher",
@@ -644,16 +644,16 @@
         },
         {
             "name": "symfony/console",
-            "version": "v5.3.7",
+            "version": "v5.3.10",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/console.git",
-                "reference": "8b1008344647462ae6ec57559da166c2bfa5e16a"
+                "reference": "d4e409d9fbcfbf71af0e5a940abb7b0b4bad0bd3"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/console/zipball/8b1008344647462ae6ec57559da166c2bfa5e16a",
-                "reference": "8b1008344647462ae6ec57559da166c2bfa5e16a",
+                "url": "https://api.github.com/repos/symfony/console/zipball/d4e409d9fbcfbf71af0e5a940abb7b0b4bad0bd3",
+                "reference": "d4e409d9fbcfbf71af0e5a940abb7b0b4bad0bd3",
                 "shasum": ""
             },
             "require": {
@@ -723,7 +723,7 @@
                 "terminal"
             ],
             "support": {
-                "source": "https://github.com/symfony/console/tree/v5.3.7"
+                "source": "https://github.com/symfony/console/tree/v5.3.10"
             },
             "funding": [
                 {
@@ -739,7 +739,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2021-08-25T20:02:16+00:00"
+            "time": "2021-10-26T09:30:15+00:00"
         },
         {
             "name": "symfony/deprecation-contracts",
@@ -2012,16 +2012,16 @@
         },
         {
             "name": "symfony/string",
-            "version": "v5.3.7",
+            "version": "v5.3.10",
             "source": {
                 "type": "git",
                 "url": "https://github.com/symfony/string.git",
-                "reference": "8d224396e28d30f81969f083a58763b8b9ceb0a5"
+                "reference": "d70c35bb20bbca71fc4ab7921e3c6bda1a82a60c"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/symfony/string/zipball/8d224396e28d30f81969f083a58763b8b9ceb0a5",
-                "reference": "8d224396e28d30f81969f083a58763b8b9ceb0a5",
+                "url": "https://api.github.com/repos/symfony/string/zipball/d70c35bb20bbca71fc4ab7921e3c6bda1a82a60c",
+                "reference": "d70c35bb20bbca71fc4ab7921e3c6bda1a82a60c",
                 "shasum": ""
             },
             "require": {
@@ -2075,7 +2075,7 @@
                 "utf8"
             ],
             "support": {
-                "source": "https://github.com/symfony/string/tree/v5.3.7"
+                "source": "https://github.com/symfony/string/tree/v5.3.10"
             },
             "funding": [
                 {
@@ -2091,7 +2091,7 @@
                     "type": "tidelift"
                 }
             ],
-            "time": "2021-08-26T08:00:08+00:00"
+            "time": "2021-10-27T18:21:46+00:00"
         }
     ],
     "packages-dev": [],