diff --git a/src/core/file.ts b/src/core/file.ts
index a8cfe79d9..e6931f366 100644
--- a/src/core/file.ts
+++ b/src/core/file.ts
@@ -276,7 +276,7 @@ function getOutDir(texPath?: string): string {
  */
 function getLangId(filename: string): string | undefined {
     const ext = path.extname(filename).toLocaleLowerCase()
-    if (ext === '.tex') {
+    if (ext === '.tex' || extraTeXExts.includes(ext)) {
         return 'latex'
     } else if (lw.constant.PWEAVE_EXT.includes(ext)) {
         return 'pweave'