diff --git a/src/wp-includes/class-wp-query.php b/src/wp-includes/class-wp-query.php
index eb68f219ce..00a085dfaa 100644
--- a/src/wp-includes/class-wp-query.php
+++ b/src/wp-includes/class-wp-query.php
@@ -2257,12 +2257,12 @@ class WP_Query {
 			if ( empty( $in_search_post_types ) ) {
 				$where .= ' AND 1=0 ';
 			} else {
-				$where .= " AND {$wpdb->posts}.post_type IN ('" . join("', '", $in_search_post_types ) . "')";
+				$where .= " AND {$wpdb->posts}.post_type IN ('" . join( "', '", array_map( 'esc_sql', $in_search_post_types ) ) . "')";
 			}
 		} elseif ( !empty( $post_type ) && is_array( $post_type ) ) {
-			$where .= " AND {$wpdb->posts}.post_type IN ('" . join("', '", $post_type) . "')";
+			$where .= " AND {$wpdb->posts}.post_type IN ('" . join("', '", esc_sql( $post_type ) ) . "')";
 		} elseif ( ! empty( $post_type ) ) {
-			$where .= " AND {$wpdb->posts}.post_type = '$post_type'";
+			$where .= $wpdb->prepare( " AND {$wpdb->posts}.post_type = %s", $post_type );
 			$post_type_object = get_post_type_object ( $post_type );
 		} elseif ( $this->is_attachment ) {
 			$where .= " AND {$wpdb->posts}.post_type = 'attachment'";