Index: src/wp-admin/includes/update-core.php
===================================================================
--- src/wp-admin/includes/update-core.php	(revision 38995)
+++ src/wp-admin/includes/update-core.php	(working copy)
@@ -746,11 +746,6 @@
 	'themes/twentyseventeen/' => '4.7',
 );
 
-// If not explicitly defined as false, don't install new default themes.
-if ( ! defined( 'CORE_UPGRADE_SKIP_NEW_BUNDLED' ) || CORE_UPGRADE_SKIP_NEW_BUNDLED ) {
-	$_new_bundled_files = array( 'plugins/akismet/' => '2.0' );
-}
-
 /**
  * Upgrades the core of WordPress.
  *
@@ -1037,6 +1032,11 @@
 		}
 	}
 
+	// If not explicitly defined as false, don't install new default themes for non-stable releases.
+	if ( ! $development_build && ( ! defined( 'CORE_UPGRADE_SKIP_NEW_BUNDLED' ) || CORE_UPGRADE_SKIP_NEW_BUNDLED ) ) {
+		$_new_bundled_files = array( 'plugins/akismet/' => '2.0' );
+	}
+
 	// Copy New bundled plugins & themes
 	// This gives us the ability to install new plugins & themes bundled with future versions of WordPress whilst avoiding the re-install upon upgrade issue.
 	// $development_build controls us overwriting bundled themes and plugins when a non-stable release is being updated