diff --git a/.travis.yml b/.travis.yml
index 31ceb337..f468f234 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -20,7 +20,7 @@ julia:
 #
 sudo: required
 before_install:
-  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then  sudo add-apt-repository ppa:pov/wkhtmltopdf  ; fi
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then  sudo add-apt-repository -y ppa:pov/wkhtmltopdf  ; fi
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then  sudo apt-get -qq update                      ; fi
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then  sudo apt-get install -y wkhtmltopdf          ; fi
   - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then  wkhtmltopdf -V                               ; fi