diff -u b/core/modules/image/image.api.php b/core/modules/image/image.api.php
--- b/core/modules/image/image.api.php
+++ b/core/modules/image/image.api.php
@@ -43,10 +43,10 @@
  *
  * This hook allows modules to alter the uri of the derivative. By implementing
  * this hook, a module can decide, for example, that a specific image style will
- * be available on a different schema. This hook is called when the image module
- * builds the uri of an image derivative.
+ * be available on a different scheme. This hook is called when the image module
+ * builds the URI of an image derivative.
  *
- * Note: If you use a special uri alteration that stores the image derivatives
+ * Note: If you use a special URI alteration that stores the image derivatives
  * outside of public://styles/{image_style}, private://styles/{image_style} or
  * even outside Drupal (for example, on a public image service like Flickr,
  * Instagram, etc.), you need to implement your own flush policy. Implementing
@@ -63,7 +63,7 @@
  *   - image_style: The \Drupal\image\ImageStyleInterface image style object.
  */
 function hook_image_style_uri_alter(&$uri, array $context) {
-  if (($name = $context['image_style']->id()) == 'watermarked_low_resolution') {
+  if (($name = $context['image_style']->id()) === 'watermarked_low_resolution') {
     $path = $context['path'];
     // Low resolution, watermarked images are available publicly, in the
     // public:// stream wrapper.