diff --git a/core/lib/Drupal/Core/Field/FieldFilteredString.php b/core/lib/Drupal/Core/Field/FieldFilteredString.php
index d41c366..8035e1a 100644
--- a/core/lib/Drupal/Core/Field/FieldFilteredString.php
+++ b/core/lib/Drupal/Core/Field/FieldFilteredString.php
@@ -77,45 +77,4 @@ public static function displayAllowedTags() {
     return '<' . implode('> <', static::allowedTags()) . '>';
   }
 
-  /**
-   * Transforms the string given an option.
-   *
-   * @param string $option
-   *   One of the following:
-   *   - upper: makes the string uppercase.
-   *   - lower: makes the string lowercase.
-   *   - ucfirst: makes the string's first character uppercase.
-   *   - ucwords: uppercase the first character of each word in the string.
-   *
-   * @return static
-   *   If the case transformation does not affect the string the same object is
-   *   returned. If it does, then a new object is returned, preserving
-   *   immutability.
-   */
-  public function caseTransform($option) {
-    $new_string = $this->string;
-    switch ($option) {
-      case 'upper':
-        $new_string = Unicode::strtoupper($this->string);
-        break;
-      case 'lower':
-        $new_string = Unicode::strtolower($this->string);
-        break;
-      case 'ucfirst':
-        $new_string = Unicode::ucfirst($this->string);
-        break;
-      case 'ucwords':
-        $new_string = Unicode::ucwords($this->string);
-        break;
-    }
-    if ($new_string !== $this->string) {
-      // The string can be considered safe because it must have been filtered
-      // during construction.
-      $new_object = new static();
-      $new_object->string = $new_string;
-      return $new_object;
-    }
-    return $this;
-  }
-
 }
diff --git a/core/modules/options/src/Plugin/views/argument/StringListField.php b/core/modules/options/src/Plugin/views/argument/StringListField.php
index 7a39b35..ddf764a 100644
--- a/core/modules/options/src/Plugin/views/argument/StringListField.php
+++ b/core/modules/options/src/Plugin/views/argument/StringListField.php
@@ -81,14 +81,9 @@ public function summaryName($data) {
     $value = $data->{$this->name_alias};
     // If the list element has a human readable name show it.
     if (isset($this->allowedValues[$value]) && !empty($this->options['summary']['human'])) {
-      $value = FieldFilteredString::create($this->allowedValues[$value]);
+      $value = $this->allowedValues[$value];
     }
-    // Else, fallback to the key.
-    else {
-      // Filtering an escaped string will not change it.
-      $value = FieldFilteredString::create(SafeMarkup::checkPlain($value));
-    }
-    return $value->caseTransform($this->options['case']);
+    return FieldFilteredString::create($this->caseTransform($value, $this->options['case']));
   }
 
 }
diff --git a/core/modules/views/src/Plugin/views/argument/ListString.php b/core/modules/views/src/Plugin/views/argument/ListString.php
index 83419eb..5b10132 100644
--- a/core/modules/views/src/Plugin/views/argument/ListString.php
+++ b/core/modules/views/src/Plugin/views/argument/ListString.php
@@ -73,14 +73,9 @@ public function summaryName($data) {
     $value = $data->{$this->name_alias};
     // If the list element has a human readable name show it,
     if (isset($this->allowed_values[$value]) && !empty($this->options['summary']['human'])) {
-      $value = FieldFilteredString::create($this->allowed_values[$value]);
+      $value = $this->allowed_values[$value];
     }
-    // else fallback to the key.
-    else {
-      // Filtering an escaped string will not change it.
-      $value = FieldFilteredString::create(SafeMarkup::checkPlain($value));
-    }
-    return $value->caseTransform($this->options['case']);
+    return FieldFilteredString::create($this->caseTransform($value, $this->options['case']));
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Field/FieldFilteredStringTest.php b/core/tests/Drupal/Tests/Core/Field/FieldFilteredStringTest.php
index c595b75..0289bd7 100644
--- a/core/tests/Drupal/Tests/Core/Field/FieldFilteredStringTest.php
+++ b/core/tests/Drupal/Tests/Core/Field/FieldFilteredStringTest.php
@@ -63,33 +63,4 @@ public function testdisplayAllowedTags() {
     $this->assertSame($expected, FieldFilteredString::displayAllowedTags());
   }
 
-  /**
-   * @covers ::caseTransform
-   * @dataProvider providertestCaseTransform
-   */
-  public function testCaseTransform($option, $test_string, $expected) {
-    $filtered_string = FieldFilteredString::create($test_string);
-    $this->assertEquals($expected, $filtered_string->caseTransform($option));
-  }
-
-  /**
-   * Provides data for testCaseTransform().
-   */
-  public function providertestCaseTransform() {
-    $data = [];
-    $data[] = [
-      'upper', 'teststring', 'TESTSTRING'
-    ];
-    $data[] = [
-      'lower', 'TESTSTRING', 'teststring'
-    ];
-    $data[] = [
-      'ucfirst', 'teststring', 'Teststring'
-    ];
-    $data[] = [
-      'ucwords', 'teststring and teststring', 'Teststring And Teststring'
-    ];
-    return $data;
-  }
-
 }