diff --git a/_bookdown.yml b/_bookdown.yml
index d084224..e9c7c2d 100644
--- a/_bookdown.yml
+++ b/_bookdown.yml
@@ -2,7 +2,7 @@ delete_merged_file: true
 new_session: yes
 
 rmd_files: [
-  "index.rmd",
+  "index.Rmd",
   "intro.Rmd",
 
   "explore.Rmd",
diff --git a/index.rmd b/index.Rmd
similarity index 100%
rename from index.rmd
rename to index.Rmd