diff --git a/.travis.yml b/.travis.yml
index e3c6dae..190001c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -103,14 +103,14 @@ matrix:
       addons:
         apt:
           sources: [llvm-toolchain-xenial-7, ubuntu-toolchain-r-test]
-          packages: [clang++-7, libc++-dev]
+          packages: [clang++-7, libc++-7-dev, libc++abi-7-dev]
       env: COMPILER=clang++-7 CXXSTD=11
     - &clang-8
       compiler: clang
       addons:
         apt:
           sources: [llvm-toolchain-xenial-8, ubuntu-toolchain-r-test]
-          packages: [clang++-8, libc++-dev]
+          packages: [clang++-8, libc++-8-dev, libc++abi-8-dev]
       env: COMPILER=clang++-8 CXXSTD=11
     - &clang-9
       compiler: clang
@@ -120,7 +120,7 @@ matrix:
             - <<: *xenial-clang
               sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main'
             - ubuntu-toolchain-r-test
-          packages: [clang++-9, libc++-dev]
+          packages: [clang++-9, libc++-9-dev, libc++abi-9-dev]
       env: COMPILER=clang++-9 CXXSTD=11
     - { <<: *gcc-5, env: COMPILER=g++-5 CXXSTD=14 }
     - { <<: *gcc-6, env: COMPILER=g++-6 CXXSTD=14 }
@@ -141,8 +141,6 @@ matrix:
     - { <<: *clang-7, env: COMPILER=clang++-7 CXXSTD=14 }
     - { <<: *clang-8, env: COMPILER=clang++-8 CXXSTD=14 }
     - { <<: *clang-9, env: COMPILER=clang++-9 CXXSTD=14 }
-    - { <<: *clang-5, env: COMPILER=clang++-5.0 CXXSTD=17 }
-    - { <<: *clang-6, env: COMPILER=clang++-6.0 CXXSTD=17 }
     - { <<: *clang-7, env: COMPILER=clang++-7 CXXSTD=17 }
     - { <<: *clang-8, env: COMPILER=clang++-8 CXXSTD=17 }
     - { <<: *clang-9, env: COMPILER=clang++-9 CXXSTD=17 }