diff --git a/wp-includes/wp-db.php b/wp-includes/wp-db.php
index a6027aa6be..5365940653 100644
--- a/wp-includes/wp-db.php
+++ b/wp-includes/wp-db.php
@@ -1207,7 +1207,7 @@ class wpdb {
 		}
 
 		foreach ( $args as $arg ) {
-			if ( ! is_scalar( $arg ) ) {
+			if ( ! is_scalar( $arg ) && ! is_null( $arg ) ) {
 				_doing_it_wrong( 'wpdb::prepare', sprintf( 'Unsupported value type (%s).', gettype( $arg ) ), '3.9.20' );
 			}
 		}