diff --git a/.travis.yml b/.travis.yml
index be74f111..0c42284f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,6 +4,7 @@ addons:
   apt:
     sources:
       - llvm-toolchain-trusty-6.0
+      - ubuntu-toolchain-r-test
     packages:
       - clang-6.0