diff --git a/core/modules/responsive_image/responsive_image.module b/core/modules/responsive_image/responsive_image.module
index de47e1f..4b7cb0d 100644
--- a/core/modules/responsive_image/responsive_image.module
+++ b/core/modules/responsive_image/responsive_image.module
@@ -226,6 +226,32 @@ function template_preprocess_responsive_image(&$variables) {
 /**
  * Helper function for template_preprocess_responsive_image().
  *
+ * @param \Drupal\Core\Image\ImageInterface $image
+ *   The image to build the <source> tags for.
+ * @param array $variables
+ *   An array with the following keys:
+ *     - responsive_image_style_id: The \Drupal\responsive_image\Entity\ResponsiveImageStyle
+ *       ID.
+ *     - width: The width of the image (if known).
+ *     - height: The height of the image (if known).
+ *     - uri: The URI of the image file.
+ * @param \Drupal\breakpoint\BreakpointInterface $breakpoint
+ *   The breakpoint for this source tag.
+ * @param array $multipliers
+ *   An array with multipliers as keys and image style mappings as values.
+ *
+ * @return \Drupal\Core\Template\Attribute[]
+ *   An array of attributes for the source tag.
+ *
+ * @deprecated in Drupal 8.3.x and will be removed before 9.0.0.
+ */
+function responsive_image_build_source_attributes(ImageInterface $image, array $variables, BreakpointInterface $breakpoint, array $multipliers) {
+  return _responsive_image_build_source_attributes($variables, $breakpoint, $multipliers);
+}
+
+/**
+ * Helper function for template_preprocess_responsive_image().
+ *
  * Builds an array of attributes for <source> tags to be used in a <picture>
  * tag. In other words, this function provides the attributes for each <source>
  * tag in a <picture> tag.
@@ -345,9 +371,6 @@ function template_preprocess_responsive_image(&$variables) {
  * See http://www.w3.org/html/wg/drafts/html/master/embedded-content.html#image-candidate-string
  * for further information.
  *
- * @param \Drupal\Core\Image\ImageInterface $image
- *   (optional) The image to build the <source> tags for. Optional and
- *   deprecated, should not be used so that it can be created when necessary.
  * @param array $variables
  *   An array with the following keys:
  *     - responsive_image_style_id: The \Drupal\responsive_image\Entity\ResponsiveImageStyle
@@ -363,12 +386,16 @@ function template_preprocess_responsive_image(&$variables) {
  * @return \Drupal\Core\Template\Attribute[]
  *   An array of attributes for the source tag.
  */
-function responsive_image_build_source_attributes(ImageInterface $image = NULL, array $variables, BreakpointInterface $breakpoint, array $multipliers) {
-  if (!$image && (empty($variables['width']) || empty($variables['height']))) {
+function _responsive_image_build_source_attributes(array $variables, BreakpointInterface $breakpoint, array $multipliers) {
+  if ((empty($variables['width']) || empty($variables['height']))) {
     $image = \Drupal::service('image.factory')->get($variables['uri']);
+    $width = $image->getWidth();
+    $height = $image->getHeight();
+  }
+  else {
+    $width = $variables['width'];
+    $height = $variables['height'];
   }
-  $width = isset($variables['width']) && !empty($variables['width']) ? $variables['width'] : $image->getWidth();
-  $height = isset($variables['height']) && !empty($variables['height']) ? $variables['height'] : $image->getHeight();
   $extension = pathinfo($variables['uri'], PATHINFO_EXTENSION);
   $sizes = array();
   $srcset = array();