diff --git a/.travis.yml b/.travis.yml
index 1d46e75..d4495ac 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,4 +6,4 @@ cache:
 
 script:
   - Rscript -e "bookdown::render_book('index.Rmd', 'bookdown::gitbook')"
-	- Rscript -e "bookdown::render_book('index.Rmd', 'bookdown::pdf_book')"
+  - Rscript -e "bookdown::render_book('index.Rmd', 'bookdown::pdf_book')"