diff --git a/php/class-wp-cli.php b/php/class-wp-cli.php
index 498b0af2..9ff85945 100644
--- a/php/class-wp-cli.php
+++ b/php/class-wp-cli.php
@@ -426,7 +426,7 @@ public function assign_user_to_coauthor( $args, $assoc_args ): void {
 			WP_CLI::error( __( 'Please specify a valid co-author login', 'co-authors-plus' ) );
 		}
 
-		$post_types = implode( "','", $coauthors_plus->supported_post_types() );
+		$post_types = "'" . implode( "','", $coauthors_plus->supported_post_types() ) . "'";
 		// phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared,WordPress.DB.DirectDatabaseQuery.DirectQuery,WordPress.DB.DirectDatabaseQuery.NoCaching
 		$posts    = $wpdb->get_col( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_author=%d AND post_type IN ({$post_types})", $user->ID ) );
 		$affected = 0;