diff --git a/core/lib/Drupal/Core/File/MimeType/MimeTypeMapper.php b/core/lib/Drupal/Core/File/MimeType/MimeTypeMapper.php
index a375001..8962393 100644
--- a/core/lib/Drupal/Core/File/MimeType/MimeTypeMapper.php
+++ b/core/lib/Drupal/Core/File/MimeType/MimeTypeMapper.php
@@ -937,6 +937,40 @@ public function addMapping($mimetype, $extension) {
   /**
    * {@inheritdoc}
    */
+  public function removeMapping($extension) {
+    // Calls ::getMapping() to make sure mappings are removed from the
+    // ::$mapping array that has been altered by modules already.
+    $this->getMapping();
+
+    $extension = strtolower($extension);
+    if (isset($this->mapping['extensions'][$extension])) {
+      unset($this->mapping['extensions'][$extension]);
+      return TRUE;
+    }
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function removeMimeType($mimetype) {
+    // Calls ::getMapping() to make sure mappings are removed from the
+    // ::$mapping array that has been altered by modules already.
+    $this->getMapping();
+
+    if (!in_array($mimetype, $this->mapping['mimetypes'])) {
+      return FALSE;
+    }
+    foreach ($this->getExtensionsForMimeType($mimetype) as $extension) {
+      $this->removeMapping($extension);
+    }
+    unset($this->mapping['mimetypes'][$mimetype]);
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function getMimeTypes() {
     return array_values($this->getMapping()['mimetypes']);
   }
diff --git a/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php b/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php
index 9b05e8c..6772cb2 100644
--- a/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php
+++ b/core/lib/Drupal/Core/File/MimeType/MimeTypeMapperInterface.php
@@ -12,18 +12,40 @@
 interface MimeTypeMapperInterface {
 
   /**
-   * Adds a mapping between a mimetype and a extension.
+   * Adds a mapping between a MIME type and an extension.
    *
    * @param string $mimetype
-   *   The mimetype the passed extension should map.
+   *   The MIME type the passed extension should map.
    * @param string $extension
-   *   The extension that should map to the passed mimetype.
+   *   The extension that should map to the passed MIME type.
    *
    * @return $this
    */
   public function addMapping($mimetype, $extension);
 
   /**
+   * Removes the mapping between a MIME type and an extension.
+   *
+   * @param string $extension
+   *   The extension to be removed from the mapping.
+   *
+   * @return bool
+   *   TRUE if the extension was present, FALSE otherwise.
+   */
+  public function removeMapping($extension);
+
+  /**
+   * Removes a MIME type and all its mapped extensions from the mapping.
+   *
+   * @param string $mimetype
+   *   The MIME type to be removed from the mapping.
+   *
+   * @return bool
+   *   TRUE if the MIME type was present, FALSE otherwise.
+   */
+  public function removeMimeType($mimetype);
+
+  /**
    * Returns known MIME types.
    *
    * @return string[]
diff --git a/core/modules/system/src/Tests/File/MimeTypeTest.php b/core/modules/system/src/Tests/File/MimeTypeTest.php
index 357fd77..ad8780f 100644
--- a/core/modules/system/src/Tests/File/MimeTypeTest.php
+++ b/core/modules/system/src/Tests/File/MimeTypeTest.php
@@ -113,5 +113,13 @@ public function testFileMimeTypeDetection() {
       $extensions = $mime_type_mapper->getExtensionsForMimeType($input);
       $this->assertIdentical($extensions, $expected, String::format('File extensions (using altered mappings) for %input are \'%output\' (expected: \'%expected\').', array('%input' => $input, '%output' => implode(', ', $extensions), '%expected' => implode(', ', $expected))));
     }
+
+    // Now test mapping removals.
+    $this->assertFalse($mime_type_mapper->removeMimeType('ready/made'), 'Unexisting MIME type not removed.');
+    $this->assertTrue($mime_type_mapper->removeMimeType('madeup/file_test_1'), 'Existing MIME type removed.');
+    $this->assertIdentical($mime_type_mapper->getExtensionsForMimeType('madeup/file_test_1'), [], 'No extensions mapped for removed MIME type.');
+    $this->assertFalse($mime_type_mapper->removeMapping('readymade'), 'Unexisting extension not removed.');
+    $this->assertTrue($mime_type_mapper->removeMapping('file_test_3'), 'Existing extension removed.');
+    $this->assertIdentical($mime_type_mapper->getExtensionsForMimeType('madeup/file_test_2'), ['file_test_2'], 'Expected extensions mapped to MIME type after extension removal.');
   }
 }