diff --git a/.travis.yml b/.travis.yml
index f03b44d..2144c95 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -31,6 +31,7 @@ matrix:
     - os: linux
       compiler: clang++
       env: TOOLSET=clang CXXSTD=03,11,14,1z
+      addons:
         apt:
           packages:
             - libstdc++-4.9-dev