diff --git a/src/Spout/Common/Escaper/XLSX.php b/src/Spout/Common/Escaper/XLSX.php
index fcb626a..7bdac43 100644
--- a/src/Spout/Common/Escaper/XLSX.php
+++ b/src/Spout/Common/Escaper/XLSX.php
@@ -27,7 +27,7 @@ class XLSX implements EscaperInterface
     public function escape($string)
     {
         $escapedString = $this->escapeControlCharacters($string);
-        $escapedString = htmlspecialchars($escapedString, ENT_QUOTES, 'utf-8');
+        $escapedString = htmlspecialchars($escapedString, ENT_QUOTES);
 
         return $escapedString;
     }
diff --git a/src/Spout/Writer/AbstractWriter.php b/src/Spout/Writer/AbstractWriter.php
index 0e9e883..c78b211 100644
--- a/src/Spout/Writer/AbstractWriter.php
+++ b/src/Spout/Writer/AbstractWriter.php
@@ -39,6 +39,7 @@ abstract class AbstractWriter implements WriterInterface
 
     /**
      * Adds data to the currently openned writer.
+     * The data must be UTF-8 encoded.
      *
      * @param  array $dataRow Array containing data to be streamed.
      *          Example $dataRow = ['data1', 1234, null, '', 'data5'];
@@ -135,6 +136,7 @@ abstract class AbstractWriter implements WriterInterface
 
     /**
      * Write given data to the output. New data will be appended to end of stream.
+     * The data must be UTF-8 encoded.
      *
      * @param  array $dataRow Array containing data to be streamed.
      *          Example $dataRow = ['data1', 1234, null, '', 'data5'];
@@ -156,6 +158,7 @@ abstract class AbstractWriter implements WriterInterface
 
     /**
      * Write given data to the output. New data will be appended to end of stream.
+     * The data must be UTF-8 encoded.
      *
      * @param  array $dataRows Array of array containing data to be streamed.
      *          Example $dataRow = [