diff --git a/.travis.yml b/.travis.yml
index 1f9e8a5b..c5ff7829 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -15,17 +15,25 @@ jobs:
         - composer install
         - composer run-script lint
     - php: 5.2
+      env:
+        - WP_VERSION=5.1.1
       dist: precise
       script:
         - ./bin/run-unit-tests.sh
     - php: 5.3
+      env:
+        - WP_VERSION=5.1.1
       dist: precise
       script:
         - ./bin/run-unit-tests.sh
     - php: 5.4
+      env:
+        - WP_VERSION=5.1.1
       script:
         - ./bin/run-unit-tests.sh
     - php: 5.5
+      env:
+        - WP_VERSION=5.1.1
       script:
         - ./bin/run-unit-tests.sh
     - php: 5.6