diff --git a/.travis.yml b/.travis.yml
index ee3882a..bd67cd3 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,11 +4,17 @@ php:
   - 5.5
   - 5.6
   - 7.0
+  - 7.1
   - hhvm
 
+env:
+  matrix:
+    - PREFER_LOWEST="--prefer-lowest"
+    - PREFER_LOWEST=""
+
 before_script:
   - travis_retry composer self-update
-  - travis_retry composer install --no-interaction --prefer-source --dev
+  - travis_retry composer install --no-interaction --prefer-source --dev $PREFER_LOWEST
   - travis_retry phpenv rehash
 
 script: