diff --git a/factors.Rmd b/factors.Rmd
index b8c9d25..5538d35 100644
--- a/factors.Rmd
+++ b/factors.Rmd
@@ -22,7 +22,7 @@ library(tidyverse)
 ### Learning more
 
 If you want to learn more about factors, I recommend reading Amelia McNamara and Nicholas Horton's paper, [*Wrangling categorical data in R*](https://peerj.com/preprints/3163/).
-This paper lays out some of the history discussed in [*stringsAsFactors: An unauthorized biography*](http://simplystatistics.org/2015/07/24/stringsasfactors-an-unauthorized-biography/) and [*stringsAsFactors = \<sigh\>*](http://notstatschat.tumblr.com/post/124987394001/stringsasfactors-sigh), and compares the tidy approaches to categorical data outlined in this book with base R methods.
+This paper lays out some of the history discussed in [*stringsAsFactors: An unauthorized biography*](https://simplystatistics.org/posts/2015-07-24-stringsasfactors-an-unauthorized-biography/) and [*stringsAsFactors = \<sigh\>*](http://notstatschat.tumblr.com/post/124987394001/stringsasfactors-sigh), and compares the tidy approaches to categorical data outlined in this book with base R methods.
 An early version of the paper helped motivate and scope the forcats package; thanks Amelia & Nick!
 
 ## Creating factors