diff --git a/src/Extension/EscaperExtension.php b/src/Extension/EscaperExtension.php
index 68adf8c2e..eebdc3a4e 100644
--- a/src/Extension/EscaperExtension.php
+++ b/src/Extension/EscaperExtension.php
@@ -282,7 +282,7 @@ function twig_escape_filter(Environment $env, $string, $strategy = 'html', $char
                     return $shortMap[$char];
                 }
 
-                $codepoint = mb_ord($char);
+                $codepoint = mb_ord($char, 'UTF-8');
                 if (0x10000 > $codepoint) {
                     return sprintf('\u%04X', $codepoint);
                 }
diff --git a/tests/Extension/EscaperTest.php b/tests/Extension/EscaperTest.php
index b7ec4065b..cf62dd1e2 100644
--- a/tests/Extension/EscaperTest.php
+++ b/tests/Extension/EscaperTest.php
@@ -182,6 +182,22 @@ class Twig_Tests_Extension_EscaperTest extends TestCase
         }
     }
 
+    public function testJavascriptEscapingConvertsSpecialCharsWithInternalEncoding()
+    {
+        $twig = new Environment($this->createMock(LoaderInterface::class));
+        $previousInternalEncoding = mb_internal_encoding();
+        try {
+            mb_internal_encoding('ISO-8859-1');
+            foreach ($this->jsSpecialChars as $key => $value) {
+                $this->assertEquals($value, twig_escape_filter($twig, $key, 'js'), 'Failed to escape: ' . $key);
+            }
+        } finally {
+            if ($previousInternalEncoding !== false) {
+                mb_internal_encoding($previousInternalEncoding);
+            }
+        }
+    }
+
     public function testJavascriptEscapingReturnsStringIfZeroLength()
     {
         $twig = new Environment($this->createMock(LoaderInterface::class));