diff --git a/core/modules/filter/filter.module b/core/modules/filter/filter.module
index ea98965..291163f 100644
--- a/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -1400,6 +1400,7 @@ function _filter_html_image_secure_process($text) {
       // Ensure the path refers to an actual image by prefixing the image source
       // with the Drupal root and running getimagesize() on it.
       $local_image_path = $local_dir . drupal_substr($src, $base_path_length);
+      $local_image_path = rawurldecode($local_image_path);
       if (@getimagesize($local_image_path)) {
         // The image has the right path. Erroneous images are dealt with below.
         continue;
diff --git a/core/modules/filter/lib/Drupal/filter/Tests/FilterHtmlImageSecureTest.php b/core/modules/filter/lib/Drupal/filter/Tests/FilterHtmlImageSecureTest.php
index d61bfa1..95e9e0d 100644
--- a/core/modules/filter/lib/Drupal/filter/Tests/FilterHtmlImageSecureTest.php
+++ b/core/modules/filter/lib/Drupal/filter/Tests/FilterHtmlImageSecureTest.php
@@ -92,6 +92,12 @@ function testImageSource() {
     $test_images = $this->drupalGetTestFiles('image');
     $test_image = $test_images[0]->filename;
 
+    // Put a test image in the files directory with special filename
+    $special_filename = 'tést fïle nàme.png';
+    $special_base_uri = str_replace($test_images[0]->filename, NULL, $test_images[0]->uri);
+    $special_image    = rawurlencode($special_filename);
+    file_unmanaged_copy($test_images[0]->uri, $special_base_uri . $special_filename);
+
     // Create a list of test image sources.
     // The keys become the value of the IMG 'src' attribute, the values are the
     // expected filter conversions.
@@ -102,6 +108,8 @@ function testImageSource() {
       $files_path . '/' . $test_image => $files_path . '/' . $test_image,
       $http_base_url . '/' . $public_files_path . '/' . $test_image => $files_path . '/' . $test_image,
       $https_base_url . '/' . $public_files_path . '/' . $test_image => $files_path . '/' . $test_image,
+      $http_base_url . '/' . $public_files_path . '/' . $special_image => $files_path . '/' . $special_image,
+      $https_base_url . '/' . $public_files_path . '/' . $special_image => $files_path . '/' . $special_image,
       $files_path . '/example.png' => $red_x_image,
       'http://example.com/' . $druplicon => $red_x_image,
       'https://example.com/' . $druplicon => $red_x_image,
diff --git a/sites/default/default.settings.php b/sites/default/default.settings.php
old mode 100644
new mode 100755