diff --git a/src/StringStream.php b/src/StringStream.php
index 8737997..85134e2 100644
--- a/src/StringStream.php
+++ b/src/StringStream.php
@@ -21,14 +21,20 @@ final class StringStream implements Stream
 {
     private string $string;
     private Position $position;
+    private bool $containsMultiBytes;
 
     /**
      * @api
      */
-    public function __construct(string $string, ?Position $position = null)
+    public function __construct(string $string, ?Position $position = null, bool $containsMultiBytes = null)
     {
         $this->string = $string;
         $this->position = $position ?? Position::initial();
+        if (null === $containsMultiBytes) {
+            $this->containsMultiBytes = \mb_strlen($string) != \strlen($string);
+        } else {
+            $this->containsMultiBytes = $containsMultiBytes;
+        }
     }
 
     /**
@@ -39,12 +45,22 @@ public function take1(): TakeResult
     {
         $this->guardEndOfStream();
 
-        $token = mb_substr($this->string, 0, 1);
+        if ($this->containsMultiBytes) {
+            $token = \mb_substr($this->string, 0, 1);
+        } else {
+            $token = \substr($this->string, 0, 1);
+        }
         $position = $this->position->advance($token);
 
+        if ($this->containsMultiBytes) {
+            $remainder = \mb_substr($this->string, 1);
+        } else {
+            $remainder = \substr($this->string, 1);
+        }
+
         return new TakeResult(
             $token,
-            new StringStream(mb_substr($this->string, 1), $position)
+            new StringStream($remainder, $position, $this->containsMultiBytes)
         );
     }