diff --git a/lisp/treesit.el b/lisp/treesit.el
index 7669ed6d18c..5a65d565236 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -987,7 +987,8 @@ If LOUDLY is non-nil, display some debugging information."
                  (end-time (current-time)))
             ;; If for any query the query time is strangely long,
             ;; switch to fast mode (see comments above).
-            (when (and (> (time-to-seconds
+            (when (and (null treesit--font-lock-fast-mode)
+                       (> (time-to-seconds
                            (time-subtract end-time start-time))
                           0.01))
               (if (> treesit--font-lock-fast-mode-grace-count 0)