diff --git a/wp-admin/includes/class-wp-filesystem-direct.php b/wp-admin/includes/class-wp-filesystem-direct.php
index e18e25775..bdad6e609 100644
--- a/wp-admin/includes/class-wp-filesystem-direct.php
+++ b/wp-admin/includes/class-wp-filesystem-direct.php
@@ -279,6 +279,11 @@ class WP_Filesystem_Direct extends WP_Filesystem_Base {
 	}
 
 	function mkdir($path, $chmod = false, $chown = false, $chgrp = false) {
+		// safe mode fails with a trailing slash under certain PHP versions.
+		$path = untrailingslashit($path);
+		if ( empty($path) )
+			$path = '/';
+
 		if ( ! $chmod )
 			$chmod = FS_CHMOD_DIR;
 
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 1afbaff1f..9d5ff245c 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -1934,7 +1934,7 @@ function wp_mkdir_p( $target ) {
 	// from php.net/mkdir user contributed notes
 	$target = str_replace( '//', '/', $target );
 
-	// safe mode fails with trailing slash under certain PHP versions.
+	// safe mode fails with a trailing slash under certain PHP versions.
 	$target = untrailingslashit($target);
 	if ( empty($target) )
 		$target = '/';