diff --git a/test/lisp/progmodes/c-ts-mode-resources/indent-preproc.erts b/test/lisp/progmodes/c-ts-mode-resources/indent-preproc.erts
index 5a4996f642e..57610b5483e 100644
--- a/test/lisp/progmodes/c-ts-mode-resources/indent-preproc.erts
+++ b/test/lisp/progmodes/c-ts-mode-resources/indent-preproc.erts
@@ -1,6 +1,7 @@
 Code:
   (lambda ()
     (c-ts-mode)
+    (setq-local indent-tabs-mode nil)
     (newline)
     (indent-for-tab-command))