diff --git a/.travis.yml b/.travis.yml
index a2281717..d39850ac 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,7 @@
 language: php
 
 php:
+  - 5.3.3
   - 5.3
   - 5.4
   - 5.5
@@ -8,7 +9,7 @@ php:
 before_script:
   - sudo apt-get -y install pypy python-sphinx graphviz
   - composer selfupdate
-  - composer install
+  - composer install --prefer-source
 
 script:
   - cd docs && make linkcheck && cd ..