diff --git a/wp-includes/wp-diff.php b/wp-includes/wp-diff.php
index f60614ad88..77f3258123 100644
--- a/wp-includes/wp-diff.php
+++ b/wp-includes/wp-diff.php
@@ -308,7 +308,7 @@ class WP_Text_Diff_Renderer_inline extends Text_Diff_Renderer_inline {
 
 	function _splitOnWords($string, $newlineEscape = "\n") {
 		$string = str_replace("\0", '', $string);
-		$words  = preg_split( '/([^\w])/', $string, -1, PREG_SPLIT_DELIM_CAPTURE );
+		$words  = preg_split( '/([^\w])/u', $string, -1, PREG_SPLIT_DELIM_CAPTURE );
 		$words  = str_replace( "\n", $newlineEscape, $words );
 		return $words;
 	}