diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 533894bc77..99722d1c7f 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -5410,7 +5410,8 @@ function wp_debug_backtrace_summary( $ignore_class = null, $skip_frames = 0, $pr
 			if ( in_array( $call['function'], array( 'do_action', 'apply_filters', 'do_action_ref_array', 'apply_filters_ref_array' ) ) ) {
 				$caller[] = "{$call['function']}('{$call['args'][0]}')";
 			} elseif ( in_array( $call['function'], array( 'include', 'include_once', 'require', 'require_once' ) ) ) {
-				$caller[] = $call['function'] . "('" . str_replace( $truncate_paths, '', wp_normalize_path( $call['args'][0] ) ) . "')";
+				$filename = isset( $call['args'][0] ) ? $call['args'][0] : '';
+				$caller[] = $call['function'] . "('" . str_replace( $truncate_paths, '', wp_normalize_path( $filename ) ) . "')";
 			} else {
 				$caller[] = $call['function'];
 			}