diff --git a/.travis.yml b/.travis.yml
index 4ef851a..fea6f9b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -25,48 +25,51 @@ env:
 
 anchors:
   libcpp: &libcpp { apt: { packages: [libc++-dev, libc++-helpers] } }
+  ubuntu-toolchain-r-test:
+    - &ubuntu-toolchain-r-test
+      sourceline: "ppa:ubuntu-toolchain-r/test"
   clang-33: &clang-33 { apt: { packages: [ "clang-3.3"]                                         } }
   clang-34: &clang-34 { apt: { packages: [ "clang-3.4"]                                         } }
-  clang-35: &clang-35 { apt: { packages: [ "clang-3.5"], sources: [ "ubuntu-toolchain-r-test" ] } }
-  clang-36: &clang-36 { apt: { packages: [ "clang-3.6"], sources: [ "ubuntu-toolchain-r-test" ] } }
-  clang-37: &clang-37 { apt: { packages: [ "clang-3.7"], sources: [ "ubuntu-toolchain-r-test" ] } }
-  clang-38: &clang-38 { apt: { packages: [ "clang-3.8"], sources: [ "ubuntu-toolchain-r-test" ] } }
-  clang-39: &clang-39 { apt: { packages: [ "clang-3.9"], sources: [ "ubuntu-toolchain-r-test" ] } }
+  clang-35: &clang-35 { apt: { packages: [ "clang-3.5"], sources: [ *ubuntu-toolchain-r-test ] } }
+  clang-36: &clang-36 { apt: { packages: [ "clang-3.6"], sources: [ *ubuntu-toolchain-r-test ] } }
+  clang-37: &clang-37 { apt: { packages: [ "clang-3.7"], sources: [ *ubuntu-toolchain-r-test ] } }
+  clang-38: &clang-38 { apt: { packages: [ "clang-3.8"], sources: [ *ubuntu-toolchain-r-test ] } }
+  clang-39: &clang-39 { apt: { packages: [ "clang-3.9"], sources: [ *ubuntu-toolchain-r-test ] } }
   clang-4:  &clang-4  { apt: { packages: [ "clang-4.0",
                                            "libstdc++-6-dev" ], sources: [ "llvm-toolchain-xenial-4.0",
-                                                                           "ubuntu-toolchain-r-test"   ] } }
+                                                                           *ubuntu-toolchain-r-test   ] } }
   clang-5:  &clang-5  { apt: { packages: [ "clang-5.0",
                                            "libstdc++-7-dev" ], sources: [ "llvm-toolchain-xenial-5.0",
-                                                                           "ubuntu-toolchain-r-test"   ] } }
+                                                                           *ubuntu-toolchain-r-test   ] } }
   clang-6:  &clang-6  { apt: { packages: [ "clang-6.0",
                                            "libc6-dbg",
                                            "libc++-dev",
                                            "libstdc++-8-dev" ], sources: [ "llvm-toolchain-xenial-6.0",
-                                                                           "ubuntu-toolchain-r-test"   ] } }
+                                                                           *ubuntu-toolchain-r-test   ] } }
   clang-7:  &clang-7  { apt: { packages: [ "clang-7",
                                            "libc6-dbg",
                                            "libc++-dev",
                                            "libstdc++-8-dev" ], sources: [ "llvm-toolchain-xenial-7",
-                                                                           "ubuntu-toolchain-r-test"   ] } }
+                                                                           *ubuntu-toolchain-r-test   ] } }
   clang-8:  &clang-8  { apt: { packages: [ "clang-8",
                                            "libc6-dbg",
                                            "libc++-dev",
                                            "libstdc++-8-dev" ], sources: [ "llvm-toolchain-xenial-8",
-                                                                           "ubuntu-toolchain-r-test"   ] } }
-  clang-9:  &clang-9  { apt: { packages: [ "clang-9" ], sources: [ "ubuntu-toolchain-r-test",
+                                                                           *ubuntu-toolchain-r-test   ] } }
+  clang-9:  &clang-9  { apt: { packages: [ "clang-9" ], sources: [ *ubuntu-toolchain-r-test,
                                { sourceline: 'deb https://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main',
                                  key_url: 'https://apt.llvm.org/llvm-snapshot.gpg.key'}                ] } }
 
-  gcc-44: &gcc-44   { apt: { packages: [ "g++-4.4" ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-46: &gcc-46   { apt: { packages: [ "g++-4.6" ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-47: &gcc-47   { apt: { packages: [ "g++-4.7" ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-48: &gcc-48   { apt: { packages: [ "g++-4.8" ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-49: &gcc-49   { apt: { packages: [ "g++-4.9" ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-5:  &gcc-5    { apt: { packages: [ "g++-5"   ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-6:  &gcc-6    { apt: { packages: [ "g++-6"   ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-7:  &gcc-7    { apt: { packages: [ "g++-7"   ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-8:  &gcc-8    { apt: { packages: [ "g++-8"   ], sources: [ "ubuntu-toolchain-r-test" ] } }
-  gcc-9:  &gcc-9    { apt: { packages: [ "g++-9"   ], sources: [ "ubuntu-toolchain-r-test" ] } }
+  gcc-44: &gcc-44   { apt: { packages: [ "g++-4.4" ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-46: &gcc-46   { apt: { packages: [ "g++-4.6" ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-47: &gcc-47   { apt: { packages: [ "g++-4.7" ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-48: &gcc-48   { apt: { packages: [ "g++-4.8" ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-49: &gcc-49   { apt: { packages: [ "g++-4.9" ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-5:  &gcc-5    { apt: { packages: [ "g++-5"   ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-6:  &gcc-6    { apt: { packages: [ "g++-6"   ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-7:  &gcc-7    { apt: { packages: [ "g++-7"   ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-8:  &gcc-8    { apt: { packages: [ "g++-8"   ], sources: [ *ubuntu-toolchain-r-test ] } }
+  gcc-9:  &gcc-9    { apt: { packages: [ "g++-9"   ], sources: [ *ubuntu-toolchain-r-test ] } }
 
 jobs:
   include: