diff --git a/wp-includes/media.php b/wp-includes/media.php
index dc49414629..9afb105268 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -1203,7 +1203,7 @@ function wp_calculate_image_srcset( $size_array, $image_src, $image_meta, $attac
 	$sources = apply_filters( 'wp_calculate_image_srcset', $sources, $size_array, $image_src, $image_meta, $attachment_id );
 
 	// Only return a 'srcset' value if there is more than one source.
-	if ( ! $src_matched || count( $sources ) < 2 ) {
+	if ( ! $src_matched || ! is_array( $sources ) || count( $sources ) < 2 ) {
 		return false;
 	}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index ba89354af0..6fb87f2244 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9.5-alpha-42668';
+$wp_version = '4.9.5-alpha-42669';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.