Index: src/wp-includes/general-template.php
===================================================================
--- src/wp-includes/general-template.php	(revision 26144)
+++ src/wp-includes/general-template.php	(working copy)
@@ -2107,7 +2107,7 @@
  * @since 3.0.0
  */
 function register_admin_color_schemes() {
-	$suffix = SCRIPT_DEBUG ? '' : '.min';
+	$suffix = defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min';
 
 	wp_admin_css_color( 'fresh', _x( 'Default', 'admin color scheme' ),
 		admin_url( "css/colors-fresh$suffix.css" ),