diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index eb3a4be051..141e3012c2 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -624,7 +624,7 @@ function get_theme_root( $stylesheet_or_template = false ) {
 	if ($stylesheet_or_template) {
 		$theme_roots = get_theme_roots();
 
-		if ( $theme_roots[$stylesheet_or_template] )
+		if ( ! empty( $theme_roots[$stylesheet_or_template] ) )
 			$theme_root = WP_CONTENT_DIR . $theme_roots[$stylesheet_or_template];
 		else
 			$theme_root = WP_CONTENT_DIR . '/themes';