diff --git a/lib/linter/linter.js b/lib/linter/linter.js
index e67574599bbe..12bf717d96ad 100644
--- a/lib/linter/linter.js
+++ b/lib/linter/linter.js
@@ -1306,7 +1306,7 @@ class Linter {
         const text = ensureText(textOrSourceCode);
         const preprocess = options.preprocess || (rawText => [rawText]);
 
-        const postprocess = options.postprocess || Array.prototype.flat.call;
+        const postprocess = options.postprocess || (messagesList => messagesList.flat());
         const filterCodeBlock =
             options.filterCodeBlock ||
             (blockFilename => blockFilename.endsWith(".js"));