diff --git a/src/Reader.php b/src/Reader.php
index 72a06b7..1471d3c 100644
--- a/src/Reader.php
+++ b/src/Reader.php
@@ -92,7 +92,11 @@ class Reader
         } elseif ($a === 'null') {
             return null;
         } elseif (substr($a, 0, 1) === '"') {
-            // remove quotes around string
+            // Remove quotes around string.
+            //
+            // Hopefully this should work correctly with Unicode strings as well,
+            // because we just want to remove one byte from beginning and end,
+            // so mb_substr should not be needed?
             return substr($a, 1, -1);
         } elseif (is_numeric($a)) {
             if (filter_var($a, FILTER_VALIDATE_INT) !== false) {
diff --git a/src/Tokenizer.php b/src/Tokenizer.php
index 705a5bf..98d0d36 100644
--- a/src/Tokenizer.php
+++ b/src/Tokenizer.php
@@ -28,8 +28,17 @@ class Tokenizer
             }
         };
 
-        for ($i = 0; $i < strlen($a); $i++) {
-            $c = substr($a, $i, 1);
+        // Use mbstring extension if available to support Unicode characters
+        if (extension_loaded('mbstring')) {
+            $lenfn = 'mb_strlen';
+            $subfn = 'mb_substr';
+        } else {
+            $lenfn = 'strlen';
+            $subfn = 'substr';
+        }
+
+        for ($i = 0; $i < $lenfn($a); $i++) {
+            $c = $subfn($a, $i, 1);
 
             if ($isString) {
                 if ($isEscape) {
diff --git a/test/TokenizerTest.php b/test/TokenizerTest.php
index af03490..f8e9bbc 100644
--- a/test/TokenizerTest.php
+++ b/test/TokenizerTest.php
@@ -103,4 +103,31 @@ class TokenizerTest extends TestCase
         $result = $tokenizer->tokenize($input);
         $this->assertSame($expected, $result);
     }
+
+    public function unicodeProvider(): array
+    {
+        return [
+            ["(∫≈♡)", ['(', '∫≈♡', ')']],
+            [
+                "αβγδ\"εζηθ\"ικλμ;νξοπ\nρς[σ τ]υ{\"φ\":\"χ\"}ψω",
+                ['αβγδ', "\"εζηθ\"", 'ικλμ', 'ρς', '[', 'σ', 'τ', ']', 'υ', '{', '"φ"', '"χ"', '}', 'ψω']
+            ],
+            ["[←↑\"→↓\"⇐⇑⇒⇓]", ['[', '←↑', '"→↓"', '⇐⇑⇒⇓', ']']],
+        ];
+    }
+
+    /**
+     * Test Unicode inputs.
+     * @dataProvider unicodeProvider
+     */
+    public function testUnicode(string $input, array $expected)
+    {
+        if (!extension_loaded('mbstring')) {
+            $this->markTestSkipped('The mbstring extension is not available.');
+        }
+
+        $tokenizer = new Tokenizer();
+        $result = $tokenizer->tokenize($input);
+        $this->assertSame($expected, $result);
+    }
 }