diff --git a/core/core-ui.el b/core/core-ui.el
index c5cd5427e..ece7a3a77 100644
--- a/core/core-ui.el
+++ b/core/core-ui.el
@@ -133,8 +133,9 @@ An omitted font size means to inherit `doom-font''s size.")
 
 (defun doom-highlight-non-default-indentation-h ()
   "Highlight whitespace at odds with `indent-tabs-mode'.
-That is, highlight tabs if the usual indentation is with spaces, and highlight
-spaces at the beginnings of lines if the usual indentation is with tabs.
+That is, highlight tabs if `indent-tabs-mode' is `nil', and highlight spaces at
+the beginnings of lines if `indent-tabs-mode' is `t'. The purpose is to make
+incorrect indentation in the current buffer obvious to you.
 
 Does nothing if `whitespace-mode' or `global-whitespace-mode' is already active
 or if the current buffer is read-only or not file-visiting."
@@ -143,11 +144,12 @@ or if the current buffer is read-only or not file-visiting."
               (null buffer-file-name))
     (require 'whitespace)
     (set (make-local-variable 'whitespace-style)
-         (let ((style (if indent-tabs-mode '(indentation) '(tabs tab-mark))))
-           (if whitespace-mode
-               (cl-union style whitespace-active-style)
-             style)))
-    (cl-pushnew 'face whitespace-style)
+         (cl-union (if indent-tabs-mode
+                       '(indentation)
+                     '(tabs tab-mark))
+                   (when whitespace-mode
+                     (remq 'face whitespace-active-style))))
+    (cl-pushnew 'face whitespace-style) ; must be first
     (whitespace-mode +1)))