diff --git a/quarto.qmd b/quarto.qmd
index eab1851..371484c 100644
--- a/quarto.qmd
+++ b/quarto.qmd
@@ -637,12 +637,12 @@ Knitr will update the results for the cached chunk whenever it detects that one
 Note that the chunks won't update if `a_very_large_file.csv` changes, because knitr caching only tracks changes within the `.qmd` file.
 If you want to also track changes to that file you can use the `cache.extra` option.
 This is an arbitrary R expression that will invalidate the cache whenever it changes.
-A good function to use is `file.info()`: it returns a bunch of information about the file including when it was last modified.
+A good function to use is `file.mtime()`: it returns when it was last modified.
 Then you can write:
 
 ``` {{r}}
 #| label: raw-data
-#| cache.extra: file.info("a_very_large_file.csv")
+#| cache.extra: !expr file.mtime("a_very_large_file.csv")
 
 rawdata <- readr::read_csv("a_very_large_file.csv")
 ```