diff --git a/wp-includes/formatting.php b/wp-includes/formatting.php
index 7c1839fa92..d55a6bd538 100644
--- a/wp-includes/formatting.php
+++ b/wp-includes/formatting.php
@@ -447,6 +447,9 @@ function sanitize_user( $username, $strict = false ) {
 	if ( $strict )
 		$username = preg_replace('|[^a-z0-9 _.\-@]|i', '', $username);
 
+	// Consolidate contiguous whitespace
+	$username = preg_replace('|\s+|', ' ', $username);
+
 	return apply_filters('sanitize_user', $username, $raw_username, $strict);
 }