diff --git a/.travis.yml b/.travis.yml
index 1940918..d65cded 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,10 +18,10 @@ git:
 #  - julia: nightly
 
 ## uncomment and modify the following lines to manually install system packages
-#addons:
-#  apt: # apt-get for linux
-#    packages:
-#    - gfortran
+addons:
+  apt: # apt-get for linux
+    packages:
+    - gnuplot
 #before_script: # homebrew for mac
 #  - if [ $TRAVIS_OS_NAME = osx ]; then brew install gcc; fi