diff --git a/wp-admin/includes/image.php b/wp-admin/includes/image.php
index 0ce97b5f76..5b667f4ab5 100644
--- a/wp-admin/includes/image.php
+++ b/wp-admin/includes/image.php
@@ -87,7 +87,7 @@ function wp_get_missing_image_subsizes( $attachment_id ) {
 
 	// Meta error?
 	if ( empty( $image_meta ) ) {
-		return $defined_sizes;
+		return $registered_sizes;
 	}
 
 	$full_width     = (int) $image_meta['width'];
@@ -379,8 +379,8 @@ function wp_generate_attachment_metadata( $attachment_id, $file ) {
 		 */
 		$fallback_sizes = apply_filters( 'fallback_intermediate_image_sizes', $fallback_sizes, $metadata );
 
-		$defined_sizes = wp_get_registered_image_subsizes();
-		$merged_sizes  = array_intersect_key( $defined_sizes, array_flip( $fallback_sizes ) );
+		$registered_sizes = wp_get_registered_image_subsizes();
+		$merged_sizes     = array_intersect_key( $registered_sizes, array_flip( $fallback_sizes ) );
 
 		// Force thumbnails to be soft crops.
 		if ( isset( $merged_sizes['thumbnail'] ) && is_array( $merged_sizes['thumbnail'] ) ) {
diff --git a/wp-includes/media.php b/wp-includes/media.php
index 20cc1b4261..e1180c28f0 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -235,7 +235,11 @@ function image_downsize( $id, $size = 'medium' ) {
 	} elseif ( $size === 'thumbnail' ) {
 		// fall back to the old thumbnail
 		$thumb_file = wp_get_attachment_thumb_file( $id );
-		$info       = getimagesize( $thumb_file );
+		$info       = null;
+
+		if ( $thumb_file ) {
+			$info = getimagesize( $thumb_file );
+		}
 
 		if ( $thumb_file && $info ) {
 			$img_url         = str_replace( $img_url_basename, wp_basename( $thumb_file ), $img_url );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index efaa7c79d4..7a7d9a2e4a 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.3-alpha-45538';
+$wp_version = '5.3-alpha-45539';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.