diff --git a/wp-admin/includes/schema.php b/wp-admin/includes/schema.php
index f9f38fdeb..5a8e40cea 100644
--- a/wp-admin/includes/schema.php
+++ b/wp-admin/includes/schema.php
@@ -651,8 +651,8 @@ function populate_network( $network_id = 1, $domain = '', $email = '', $site_nam
 	$allowed_themes = array( $stylesheet => true );
 	if ( $template != $stylesheet )
 		$allowed_themes[ $template ] = true;
-	if ( WP_FALLBACK_THEME != $stylesheet && WP_FALLBACK_THEME != $template )
-		$allowed_themes[ WP_FALLBACK_THEME ] = true;
+	if ( WP_DEFAULT_THEME != $stylesheet && WP_DEFAULT_THEME != $template )
+		$allowed_themes[ WP_DEFAULT_THEME ] = true;
 
 	if ( 1 == $network_id ) {
 		$wpdb->insert( $wpdb->site, array( 'domain' => $domain, 'path' => $path ) );
diff --git a/wp-admin/includes/upgrade.php b/wp-admin/includes/upgrade.php
index 34a0803a1..1373b6584 100644
--- a/wp-admin/includes/upgrade.php
+++ b/wp-admin/includes/upgrade.php
@@ -1623,7 +1623,7 @@ function make_site_theme_from_oldschool($theme_name, $template) {
 		if ($oldfile == 'index.php') { // Check to make sure it's not a new index
 			$index = implode('', file("$oldpath/$oldfile"));
 			if (strpos($index, 'WP_USE_THEMES') !== false) {
-				if (! @copy(WP_CONTENT_DIR . '/themes/'.WP_FALLBACK_THEME.'/index.php', "$site_dir/$newfile"))
+				if (! @copy(WP_CONTENT_DIR . '/themes/' . WP_DEFAULT_THEME . '/index.php', "$site_dir/$newfile"))
 					return false;
 				continue; // Don't copy anything
 				}
@@ -1683,7 +1683,7 @@ function make_site_theme_from_oldschool($theme_name, $template) {
  */
 function make_site_theme_from_default($theme_name, $template) {
 	$site_dir = WP_CONTENT_DIR . "/themes/$template";
-	$default_dir = WP_CONTENT_DIR . '/themes/'.WP_FALLBACK_THEME;
+	$default_dir = WP_CONTENT_DIR . '/themes/' . WP_DEFAULT_THEME;
 
 	// Copy files from the default theme to the site theme.
 	//$files = array('index.php', 'comments.php', 'comments-popup.php', 'footer.php', 'header.php', 'sidebar.php', 'style.css');
@@ -1779,7 +1779,7 @@ function make_site_theme() {
 
 	// Make the new site theme active.
 	$current_template = __get_option('template');
-	if ($current_template == WP_FALLBACK_THEME) {
+	if ($current_template == WP_DEFAULT_THEME) {
 		update_option('template', $template);
 		update_option('stylesheet', $template);
 	}
diff --git a/wp-includes/default-constants.php b/wp-includes/default-constants.php
index f44fb6701..222eb3df5 100644
--- a/wp-includes/default-constants.php
+++ b/wp-includes/default-constants.php
@@ -286,18 +286,12 @@ function wp_templating_constants( ) {
 	/**
 	 * Slug of the default theme for this install.
 	 * Used as the default theme when installing new sites.
+	 * Will be used as the fallback if the current theme doesn't exist. 
 	 * @since 3.0.0
 	 */
 	if ( !defined('WP_DEFAULT_THEME') )
 		define( 'WP_DEFAULT_THEME', 'twentyten' );
 
-	/**
-	 * Slug of the fallback theme for this install.
-	 * Will be used as the fallback if the current theme doesn't exist.
-	 * @since 3.0.0
-	 */
-	if ( !defined('WP_FALLBACK_THEME') )
-		define( 'WP_FALLBACK_THEME', WP_DEFAULT_THEME );
 }
 
 ?>
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index c58a9f51c..086542353 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -1207,13 +1207,13 @@ function switch_theme($template, $stylesheet) {
 /**
  * Checks that current theme files 'index.php' and 'style.css' exists.
  *
- * Does not check the fallback theme. The fallback theme should always exist.
+ * Does not check the default theme, which is the fallback and should always exist.
  * Will switch theme to the fallback theme if current theme does not validate.
  * You can use the 'validate_current_theme' filter to return FALSE to
  * disable this functionality.
  *
  * @since 1.5.0
- * @see WP_FALLBACK_THEME
+ * @see WP_DEFAULT_THEME
  *
  * @return bool
  */
@@ -1222,13 +1222,13 @@ function validate_current_theme() {
 	if ( defined('WP_INSTALLING') || !apply_filters( 'validate_current_theme', true ) )
 		return true;
 
-	if ( get_template() != WP_FALLBACK_THEME && !file_exists(get_template_directory() . '/index.php') ) {
-		switch_theme( WP_FALLBACK_THEME, WP_FALLBACK_THEME );
+	if ( get_template() != WP_DEFAULT_THEME && !file_exists(get_template_directory() . '/index.php') ) {
+		switch_theme( WP_DEFAULT_THEME, WP_DEFAULT_THEME );
 		return false;
 	}
 
-	if ( get_stylesheet() != WP_FALLBACK_THEME && !file_exists(get_template_directory() . '/style.css') ) {
-		switch_theme( WP_FALLBACK_THEME, WP_FALLBACK_THEME );
+	if ( get_stylesheet() != WP_DEFAULT_THEME && !file_exists(get_template_directory() . '/style.css') ) {
+		switch_theme( WP_DEFAULT_THEME, WP_DEFAULT_THEME );
 		return false;
 	}