diff --git a/.changeset/great-apples-whisper.md b/.changeset/great-apples-whisper.md
new file mode 100644
index 0000000..56dd235
--- /dev/null
+++ b/.changeset/great-apples-whisper.md
@@ -0,0 +1,5 @@
+---
+"typescript-eslint-parser-for-extra-files": patch
+---
+
+fix: bug for useCaseSensitiveFileNames
diff --git a/src/ts.ts b/src/ts.ts
index 42aedbe..20c9b8e 100644
--- a/src/ts.ts
+++ b/src/ts.ts
@@ -363,8 +363,8 @@ function distinctArray(...list: (string | null | undefined)[]) {
   return [
     ...new Set(
       ts.sys.useCaseSensitiveFileNames
-        ? list.map((s) => s?.toLowerCase())
-        : list
+        ? list
+        : list.map((s) => s?.toLowerCase())
     ),
   ].filter((s): s is string => s != null);
 }