diff --git a/composer.json b/composer.json
index aa5ded6f..f5ee58ce 100644
--- a/composer.json
+++ b/composer.json
@@ -32,6 +32,7 @@
         "laminas/laminas-stdlib": "^2.7 || ^3.0",
         "laminas/laminas-validator": "^2.10.2",
         "laminas/laminas-zendframework-bridge": "^1.0",
+        "symfony/polyfill-mbstring": "^1.12.0",
         "true/punycode": "^2.1"
     },
     "require-dev": {
diff --git a/src/Header/ContentDisposition.php b/src/Header/ContentDisposition.php
index 60031f7d..f3b4dad2 100644
--- a/src/Header/ContentDisposition.php
+++ b/src/Header/ContentDisposition.php
@@ -154,26 +154,34 @@ public function getFieldValue($format = HeaderInterface::FORMAT_RAW)
                 }
             } else {
                 // Use 'continuation' per RFC 2231
-                $maxValueLength = strlen($value);
-                do {
-                    $maxValueLength = ceil(0.6 * $maxValueLength);
-                } while ($maxValueLength > self::MAX_PARAMETER_LENGTH);
-
                 if ($valueIsEncoded) {
-                    $encodedLength = strlen($value);
                     $value = HeaderWrap::mimeDecodeValue($value);
-                    $decodedLength = strlen($value);
-                    $maxValueLength -= ($encodedLength - $decodedLength);
                 }
 
-                $valueParts = str_split($value, $maxValueLength);
                 $i = 0;
-                foreach ($valueParts as $valuePart) {
-                    $attributePart = $attribute . '*' . $i++;
-                    if ($valueIsEncoded) {
-                        $valuePart = $this->getEncodedValue($valuePart);
+                $fullLength = mb_strlen($value, 'UTF-8');
+                while ($fullLength > 0) {
+                    $attributePart = $attribute . '*' . $i++ . '="';
+                    $attLen = mb_strlen($attributePart, 'UTF-8');
+
+                    $subPos = 1;
+                    $valuePart = '';
+                    while ($subPos <= $fullLength) {
+                        $sub = mb_substr($value, 0, $subPos, 'UTF-8');
+                        if ($valueIsEncoded) {
+                            $sub = $this->getEncodedValue($sub);
+                        }
+                        if ($attLen + mb_strlen($sub, 'UTF-8') >= self::MAX_PARAMETER_LENGTH) {
+                            $subPos--;
+                            break;
+                        }
+                        $subPos++;
+                        $valuePart = $sub;
                     }
-                    $result .= sprintf(';%s%s="%s"', Headers::FOLDING, $attributePart, $valuePart);
+
+                    $value = mb_substr($value, $subPos, null, 'UTF-8');
+                    $fullLength = mb_strlen($value, 'UTF-8');
+                    $result .= ';' . Headers::FOLDING . $attributePart . $valuePart . '"';
                 }
             }
         }
diff --git a/test/Header/ContentDispositionTest.php b/test/Header/ContentDispositionTest.php
index 5a4b2140..41f1d842 100644
--- a/test/Header/ContentDispositionTest.php
+++ b/test/Header/ContentDispositionTest.php
@@ -190,12 +190,20 @@ public function setDispositionProvider(): array
         // @codingStandardsIgnoreStart
         $foldingFieldValue = "attachment;\r\n filename=\"this-test-filename-is-long-enough-to-flow-to-two-lines.txt\"";
         $foldingHeaderLine = "Content-Disposition: $foldingFieldValue";
-        $continuationFieldValue = "attachment;\r\n filename*0=\"this-file-name-is-so-long-that-it-does-not-even\";\r\n filename*1=\"-fit-on-a-whole-line-by-itself-so-we-need-to-sp\";\r\n filename*2=\"lit-it-with-value-continuation.txt\"";
+        $continuationFieldValue = "attachment;\r\n filename*0=\"this-file-name-is-so-long-that-it-does-not-even-fit-on-a-whole-\";\r\n filename*1=\"line-by-itself-so-we-need-to-split-it-with-value-continuation.t\";\r\n filename*2=\"xt\"";
         $continuationHeaderLine = "Content-Disposition: $continuationFieldValue";
 
         $encodedHeaderLine = 'Content-Disposition: attachment; filename="=?UTF-8?Q?=C3=93?="';
         $encodedFieldValue = 'attachment; filename="Ó"';
 
+        $multibyteFilename = '办公.xlsx';
+        $multibyteFieldValue = "attachment;\r\n filename=\"=?UTF-8?Q?=E5=8A=9E=E5=85=AC.xlsx?=\"";
+        $multibyteHeaderLine = "Content-Disposition: $multibyteFieldValue";
+
+        $multibyteContinuationFilename = '办公用品预约Apply for office supplies online.xlsx';
+        $multibyteContinuationFieldValue = "attachment;\r\n filename*0=\"=?UTF-8?Q?=E5=8A=9E=E5=85=AC=E7=94=A8=E5=93=81=E9=A2=84?=\";\r\n filename*1=\"=?UTF-8?Q?=E7=BA=A6Apply=20for=20office=20supplies=20online.x?=\";\r\n filename*2=\"=?UTF-8?Q?lsx?=\"";
+        $multibyteContinuationHeaderLine = "Content-Disposition: $multibyteContinuationFieldValue";
+
         return [
             // Description => [$disposition, $parameters, $fieldValue, toString()]
             'inline with no parameters' => ['inline', [], 'inline', 'Content-Disposition: inline'],
@@ -218,8 +226,20 @@ public function setDispositionProvider(): array
             'UTF-8 continuation' => [
                 'attachment',
                 ['filename' => 'this-file-name-is-so-long-that-it-does-not-even-fit-on-a-whole-line-by-itself-so-we-need-to-split-it-with-value-continuation.also-UTF-8-characters-hērē.txt'],
-                "attachment;\r\n filename*0=\"this-file-name-is-so-long-that-it-does-not-even-fit-on-a-\";\r\n filename*1=\"whole-line-by-itself-so-we-need-to-split-it-with-value-co\";\r\n filename*2=\"ntinuation.also-UTF-8-characters-hērē.txt\"",
-                "Content-Disposition: attachment;\r\n filename*0=\"=?UTF-8?Q?this-file-name-is-so-long-that-it-does-not-ev?=\";\r\n filename*1=\"=?UTF-8?Q?en-fit-on-a-whole-line-by-itself-so-we-need-t?=\";\r\n filename*2=\"=?UTF-8?Q?o-split-it-with-value-continuation.also-UTF-8?=\";\r\n filename*3=\"=?UTF-8?Q?-characters-h=C4=93r=C4=93.txt?=\"",
+                "attachment;\r\n filename*0=\"this-file-name-is-so-long-that-it-does-not-even-fit-on-a-whole-\";\r\n filename*1=\"line-by-itself-so-we-need-to-split-it-with-value-continuation.a\";\r\n filename*2=\"lso-UTF-8-characters-hērē.txt\"",
+                "Content-Disposition: attachment;\r\n filename*0=\"=?UTF-8?Q?this-file-name-is-so-long-that-it-does-not-even-fit?=\";\r\n filename*1=\"=?UTF-8?Q?-on-a-whole-line-by-itself-so-we-need-to-split-it-w?=\";\r\n filename*2=\"=?UTF-8?Q?ith-value-continuation.also-UTF-8-characters-h?=\";\r\n filename*3=\"=?UTF-8?Q?=C4=93r=C4=93.txt?=\"",
+            ],
+            'UTF-8 multibyte' => [
+                'attachment',
+                ['filename' => $multibyteFilename],
+                "attachment; filename=\"$multibyteFilename\"",
+                $multibyteHeaderLine,
+            ],
+            'UTF-8 multibyte continuation' => [
+                'attachment',
+                ['filename' => $multibyteContinuationFilename],
+                "attachment;\r\n filename=\"$multibyteContinuationFilename\"",
+                $multibyteContinuationHeaderLine,
             ],
         ];
         // @codingStandardsIgnoreEnd