diff --git a/wp-includes/media.php b/wp-includes/media.php
index b3a7ac7cd2..44e18f4a20 100644
--- a/wp-includes/media.php
+++ b/wp-includes/media.php
@@ -767,7 +767,7 @@ function wp_get_attachment_image($attachment_id, $size = 'thumbnail', $icon = fa
 		$attachment = get_post($attachment_id);
 		$default_attr = array(
 			'src'	=> $src,
-			'class'	=> "attachment-$size_class size-$size",
+			'class'	=> "attachment-$size_class size-$size_class",
 			'alt'	=> trim(strip_tags( get_post_meta($attachment_id, '_wp_attachment_image_alt', true) )), // Use Alt field first
 		);
 		if ( empty($default_attr['alt']) )
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 91a44d4d08..4775d31a0c 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34656';
+$wp_version = '4.4-alpha-34657';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.